In OTL, Edward IV's brother Richard Duke of Gloucester became regent, and then King Richard III, Edward and, his brother disappeared (the Princes in the Tower).
Alternative histories (see under Richard III for more possibilities):
- Edward V succeeds to the throne and is allowed to retain it, with Richard of Gloucester as regent.
- Edward V succeeds to the throne, and his mother and her brothers wrest control from Richard of Gloucester.
If Edward V did not succeed, but survived, with or without his brother, he could launch a counter-coup from within England, or from Scotland, France, or elsewhere.
There is also the alien abduction possibility.