He never really wanted to be King, no matter how happy he seemed. Edmund Pevensie could remember a time, a time when he served under a King, the Once and Future King.
Of course, it wasn't he that served, no, it had been Merlin. Merlin Ambrosius, Emrys Myrddin, handservant of Arthur Pendragon.
Narnia brought back the memories, and soon enough it brought back the magic he once had before. He told no-one, not even Lucy, who would have delighted and celebrated. Magic was prized.
The only one who knew was Aslan, and even then they said nothing of it, not until that day when he and Lucy and Eustace were about to return to their own world. They had a conversation of the minds, and he knew. Edmund knew he could no longer be who he was. The magic had returned with him the first time, and the second time, but this was his final time. Once he left for his own world, the magic would leave to stay in Narnia.
So he only had one request when they spoke that brief time.
'Make me forget.'