Crossed Swords (1977)

Tom Canty (Mark Lester) is a poor English boy who bears a remarkable resemblance to Edward, Prince of Wales (Mark Lester) and son of King Henry VIII (Charlton Heston). The two boys meet and decide to play a joke on the court by dressing in each other's clothes, but the plan goes awry when they are separated and each must live the other's life.