If the secret is going to be the "twist" of the movie's plot, it won't work. But if the emphasis is place on the theme of trusting in Aslan in difficult times, then it will work. It will work because Eustace and Jill must put their faith in Aslan that the crazy, insane person in front of them is Rilian. They have to choose to free him despite their fears. That's the other thing that has to work: Rilian must be convincing as a lunatic for the audience. The filmmakers must make not just the children doubt, but the audience as well, despite their strong suspicion that he is Rilian.

If they do want to make it a surprise, they could have multiple knights that could potentionally be Rillian. But that would mean spending time setting up two possible Rillians and would inevitably lead to unwanted changes.

If there's a flashback of Rilian trying to avenge his mother and meeting the Lady of the Green Kirtle, the audience will know what Rilian looks like and will immediately recognize Rilian in Underland.

There are a couple ways I can think of for handling this:

1) Skip the flashback. So far, the first three movies have shied away from flashbacks, but with the new production company etc., I'm not sure if this trend will necessarily continue. The easiest way to skip the flashback would be to deliver the background information via the Parliament of Owls. The problem I have with this is that it goes against film being a visual medium. It would be boring to watch a scene of characters explaining backstory (unlike in a book when it can actually be quite interesting).

2) Disguise Rilian in Underland. The BBC SC gave Rilian a beard and a mask in Underland, so the audience wouldn't recognize him. I don't think I'd like something obscuring Rilian's face, because we might not be able to see his facial expressions as well.

3) As Rose-Tree Dryad suggested in the "Differences You Actually Want" thread, the flashback could be hazy, perhaps because Jill is drifting in and out of sleep during the Owl's meeting. There are other ways of hiding Rilian's face during the flashback as well.

4) An idea I had would be to have images showing Rilian's backstory during the opening credits. There could be a voice-over, but I think it would be better for the images to speak for themselves. The images themselves could be carvings on a wall (like in Aslan's How), stained glass, a storybook (though this might be too cliche at this point), pictures resembling Pauline Bayne's illustrations etc. Once the opening credits were over, the movie would open with Experiment House and go on from there. The owls could still explain Rilian's story, but they wouldn't have to go as in-depth as they normally would, because the audience will remember the opening credits. That way Rilian's backstory would still be explained visually, but the audience wouldn't recognize Rilian in Underland because he was stylized during the opening credits.

For me, the climax of the book is when they decide to trust Aslan's signs and cut the prince's bonds. I believe it is primarily through Puddleglum's example that Jill's emotional wounds start to heal, and she regains the ability to trust again.

I think that makes a lot of sense, and I think it really does need to be the climax and focus of that entire exchange, since the theme here isn't twist but trust.

It's also an interesting parallel to the beginning of the story when Jill has to choose to go drink the water in the stream, even though she is certain the Lion will kill her. It would be great if they could emphasize that overarching theme in the film and the development of Jill's character—going from the girl who only just began to trust because she's dying of thirst to someone who chose to undo the binds of a madman in order to finally follow the signs given by Aslan. I think it really shows her character arc and I definitely agree that Puddleglum's example was an integral part of that process.

I just hope the actor who plays Rilian is extremely convincing as a raving lunatic.

If they do want to make it a surprise, they could have multiple knights that could potentionally be Rillian. But that would mean spending time setting up two possible Rillians and would inevitably lead to unwanted changes.

Or they could have multiple suits of armor, enchanted and animated by LotGK, that are nothing but air on the inside. Or even skeletons, for that matter, since we're drawing inspiration from Puddleglum's suspicions of the Black Knight.

"Many fall down, and few return to the sunlit lands...."

I imagine that could be quite interesting, if they decide that they need a device to make the audience question who really is Rilian. I'm not sure if there could be any thematic or plot ramifications, though; I haven't had a chance to think it through.

An idea I had would be to have images showing Rilian's backstory during the opening credits. There could be a voice-over, but I think it would be better for the images to speak for themselves. The images themselves could be carvings on a wall (like in Aslan's How), stained glass, a storybook (though this might be too cliche at this point), pictures resembling Pauline Bayne's illustrations etc.

I like the idea of the backstory being shown with carvings on a wall, as if in a cavern and lit by lamplight, because it foreshadows Underland. I like the mental image of stained glass as well, though I think it would also be great if it looked as though it belonged in Underland, too—Lewis tells us that there are windows in the Dark Castle but very few are lighted. I think showing a series of stained glass scenes illuminated by a lone lamplight carried by the darkened windows could be a really effective and mysterious way to tell the story and begin the film.

(Sorry if that last bit is a little off-topic!)

If there's a flashback of Rilian trying to avenge his mother and meeting the Lady of the Green Kirtle, the audience will know what Rilian looks like and will immediately recognize Rilian in Underland.

They could easily just have Rilian appear as a child. Maybe 12 years old?

I think the flashbacks should be sort of a random dream-like sequence and perhaps in no particular order. The viewer should only get a vague idea of what happened to Rilian until the very end when Rilian is disenchanted and able to say what happened. Until that point we should only have clues. Like piecing together a mystery.

a backstage of Rilian and Caspian s wife would be awesome(think of a glorious scene of Liliandil being transferred dead to Cair Paravel with all the honours). Also they can use the Green Witch way more tha she is used in the book.I suspect something of her past being shown and explained. Lewis in the book pointed out she is one of the some crew. Is she one of Jadis sister that survived somehow ?

Rilian doesn't have to appear noticeably in any flashback. He could be indistinguishable from all the other young men who are about his age on the maying party, and the centre of attention should be on Caspian's Queen and the snake, and on Caspian's reaction to the death.

^ If Rilian wasn't featured prominently in the flashback, wouldn't that defeat the purpose of the flashback though? The main idea of the information given during the Parliament of Owls is what happened to Prince Rilian. Rilian's mother's death is only important because it causes Rilian to ride off to avenge her death, which causes him to meet and fall under the spell of the Lady of the Green Kirtle.

Impending Doom, Rilian needs to be infatuated by the Lady of the Green Kirtle, so I'm not sure if having Rilian being a child would make sense. The idea of the characters receiving bits of information at a time is an interesting idea though. I could see that working.

i mean the moment Rilian starts to remember its past , the sun ,the open world and while the green witch is bewitching the characters with her tricks and how was the life in Cair Paravel should be the emphasis of the scene. He will go lunatic as scenes of the past comes randomly to his mind. If the director focus there, it will be a great result. So the battle inside of Rilian s head between the rememberence and the forgetence will be the high peak of the movie. They need a very good actor for this scene to play Rilian.

Maybe they should make a virtue out of necessity when adapting The Silver Chair for the big screen, and instead of trying to conceal the Prince's identity until the moment when he's bound to the Chair and cries out, "In the name of Aslan," make it obvious to everyone (including Eustace, Jill and Puddleglum) that this weird knight is the Prince, but convince them and the audience that he's turned evil. So the task takes on a twist, once they find the Prince, of how they can turn him back to good.

To be honest, ever since I first read the book I've thought that the notion that the Queen's enchantment over the Prince "wears off" every day and he has to be bound to the Silver Chair to re-establish it, to be a weak plot device. If she was unable to create a permanent hold over him, you would imagine that she wouldn't let him out of her sight for longer than a few hours, in case he broke free from the Chair (even without help from outsiders) and the enchantment wore off completely. And why is the Chair significant? Did it feature in the Queen's initial establishment of the enchantment?

Perhaps the appearance of Eustace and Jill - children from the Other World, whom his father would have told him about when he was young - and especially Puddleglum, a Narnian creature, may have started to make lost memories resurface, before he gets bound to the Chair. Perhaps the Queen's enchantment was permanent until they met the children and Puddleglum above ground, and that started to produce cracks in the Queen's magic. The Queen then used the Chair on him every day from then on, but after a while she became complacent and believed that her magic had re-asserted itself, and so she felt confident that she could leave him alone, have the gnomes bind him to the Chair and everything would be fine.

I don't remember how surprised I was by discovering the Black Knight was really Rilian. I was pretty young when I was first read SC and I doubt I saw it coming.

I do remember being very startled by the LotGK actually turning into the serpent. I guess I always figured she had summoned the snake that killed the Queen rather than actually being the serpent.

At any rate, I think that it could be made to be a surprise, especially for a younger audience. Some possibilities would be if you cast a young Prince Rilian for the flashback and then credited the "Black Knight" in the credits for the older Prince Rilian. That could potentially throw some people. I think if they cast Rilian to look like his star mother rather than his Telmarine father, that could potentially throw some people.

Anyways, just some random thoughts.

Or maybe a teenaged Rilian looking like his star mother, and an older Rilian looking more like his father?

That might work.

You know, something that I think is definitely worth considering is that from the time the Lady of the Green Kirtle lured Rilian away, he did not come into contact with sunlight for ten years. Even when she would let him go up into Overland to let his eyes adjust, his skin was completely covered with the black armor.

If we imagine that Rilian took after his mother and assume that he enjoyed spending plenty of time outside, as any young man would, then originally his hair was probably very fair and his skin very tan. After he has spent so much time away from the sun, however, I would think he'd look very different indeed—as pale as could be, and his hair would likely darken quite a bit from lack of sun to bring out highlights.

I also concur with the idea that they could have young Rilian be in his late teens, with a much older actor to play the man that Jill, Eustace and Puddleglum meet in Underland. Obviously, there would still need to be a great deal of similarity in terms of face structure and eye color, but with the complexion, hair color and personality so different, it could still really throw the audience for a loop.

Another thing that the audience would figure out long before the characters do, is the connection between the green serpent, the green lady who lures away Rillian, and the green lady on the horse. I dare say most people will already know who the black knight is as well. Some of the ideas for flash backs already mentioned in the discussion might help with that though. I really like the idea of finally seeing the flashback of what happened between Rillian and the Lady when he is raving (we would already know about him chasing the serpent, just not what made him disappear). Then when LotGK walks the "OH NO!" factor would be greatly increased because it is fresh in the mind.
Oh, and by the way we probably will see green smoke when the green lady throws green powder on the fire. (the green powder is my addition) I mean how else are they going to show the children and Puddleglum and Rillian being affected by it?! Sorry for being off topic glumPuddle, but I really couldn't resist!

A few times in the Chronicles there are plot elements that appear to be twists that the reader generally knows beforehand. What sells it is the vivid characters. It may not be twist to us, but it is to them and if we care enough about them, the scene is just as powerful. Lewis does a great job of this, yet it would be difficult to pull off on film because movie-goers are so used to twists they might find it an unsurprising one, as many have said, and miss the real purpose of the scene. Perhaps rather than obscuring Rilian's identity, it should be made quite plain to the audience that this man is the lost prince and the lady is the serpent while the others don't know it yet. Then really focus on their uncertainty as in the book. Just an idea. Haven't thought it through fully.

As for a flashback, I'm not sure. I personally would love a simple monologue from an elderly owl in a dark tower but I doubt that would go over well, especially in a children's movie. Got to keep it visually interesting. Perhaps, if a flashback is needed for the prince's story, an animated sequence like the tale of the three brothers in The Deathly Hallows, though maybe less jarring. Something like what The Rose-Tree Dryad said, told through stained-glass and tapestries, but have them move in a stylized animation.

I really hope they don't give us a straight-up flashback, but it could be done well.