I don't think I need to say this, but the person talking to Amber in her dream is Aslan.

Chapter 6: Strange Dreams

"Amber, it's time to prepare yourself."

"Prepare myself for what?" Amber asked.

"The Kings and Queens will soon be leaving. They will be gone for a very long time, and you have to be prepared."

"Where will they go?"

"The Kings and Queens of the Golden Age are not natives to Narnia. They must return to their own world."

"What! But Narnia needs them here!"

"You are right. Narnia needs her Kings and Queens right now. But they each have lives in their own world. And they must learn to live those lives."

"But what will Narnia do without their Kings and Queens?"

"Narnia will have you. When the Kings and Queens leave, Narnia will look to you to lead them. Though I do not wish it, Narnia will have dark times coming. You will need to keep her strong."

"But… I'm not their Queen. I-"

"You are a true Narnian, Amber. And you must pass that on to others."

"Will… will the Pevensies come back?"

"If Narnia needs them, they will come. Do not fret, Child. You will never be alone, as long as you have faith. All will happen and all will be explained in good time. This I promise you. Now, sleep, Child. Sleep in peace until the morning comes."

"Amber." Amber jumped awake, automatically transforming into a Girl. She squinted; why was it so bright? And why was she laying on sand? Oh. That's right, she had snuck down to the beach.

"Amber."

"What?" Amber asked irritably, looking up at the figure standing above her. He was standing in front of the sun, so all she could see was a silhouette- but she knew who it was. "Peter, what do you want?"

"Would you like to explain why you, Susan, Edmund, Lucy, and Corin are out here?"

"Ugh. You woke me up for that? Isn't it obvious? We didn't want to sleep inside, so we decided to come out here. You had already gone to sleep, so we just… went. Could you move to the other side so I don't have to stare into the sun?"

"Amber, did you even stop to think that there could be dangers out here?"

"I'm not a little girl, Pete. If you haven't noticed, I'm a Tiger. Even if someone had managed to sneak up on us, I could have killed them in a moment, had I chosen to."

"I managed to sneak up on you," Peter said. "And I'm still alive."

"Because I want you to be," Amber replied, getting up.

"Who even thought of this?"

"Lucy suggested it when I said I couldn't sleep."

"And how did Lucy get it in her head?"

"I don't know. She said that if you listened to the sound of the waves crashing on the beach coupled with the songs of the Merpeople while staring up at the stars, it would lull you sleep."

"How would she know that?" Peter asked. Amber just shrugged, though she knew the answer. She wouldn't be the one to cause Lucy grief. She looked around as the culprit in question woke up, stretching.

"Morning, Amber," Lucy said sleepily. "Didn't I tell you? Best night ever."

"Good morning, Lucy," Peter said sternly. Lucy's eyes nearly popped out of her head when she saw her older brother.

"Uh… hi, Peter…"

"I'll talk with you later. Right now we should get the rest up. King Lune's leaving today, so Corin needs to be awake and ready soon to see his father off." Peter used his foot to shake Edmund awake. Lucy kneeled and woke Corin, and Susan was waking up as well. Each of them started when they saw Peter, then looked down guiltily. They knew that they were in trouble, so they just stood around, shuffling their feet. Amber glanced at Peter. He really did make an imposing figure, with his broad chest and his arms crossed, and that stern look on his face…

"I am shocked at each of you," he said, "particularly you three." Here he faced Amber, Susan, and Edmund. "You especially should know better."

"We were perfectly safe," Susan defended. "Amber was here, and Edmund and Corin… if anyone had tried to hurt us…"

"I know that perfectly well. But that's not what I meant. I'm shocked that not one of you thought to come get me!" Everyone visibly relaxed as they realized that Peter wasn't really angry with them. He laughed; obviously, the High King was amused by the contriteness of his consorts. "Come up to breakfast, then get cleaned up. You all have sand in your hair and clothes…"