Prince Caspian was raised by his uncle, Miraz. During his childhood, he heard all sorts of wonderful stories about Aslan, talking animals, and Old Narnia from his nurse.
One day, Caspian tries to share these tales with his uncle. Hearing this "nonsense" gets Miraz fuming mad (4.12). Poor Nurse is fired toot-sweet.
She's replaced by a tutor, one Dr. Cornelius. We have no idea what he received his PhD in, but he lets on that he knows all sorts of things about Narnia's history.
A few days later, Cornelius takes Caspian to the top of the Great Tower for some late night stargazing.
There, he gives Caspian the most interesting history lesson ever.
He tells the young prince about Old Narnia: fauns, centaurs, talking animals, walking trees, the High Kings and Queens and, of course, Aslan. Cornelius even lets on that he's a half-dwarf, making him twice as awesome in Caspian's eyes.
Cornelius cuts the lesson just when things get interesting (boo!), saying they should return before someone notices they're gone.