^Not quite the same but when they did The Road to Coronation Street a few years ago, the son of William Roache (Ken Barlow) played the young William. He was almost concurrently playing Ken's long-lost grandson in Corrie, opposite William.
Adding to the confusion, William's other son Linus was appearing as Ken's son and the father of the long-lost grandson. Linus in the 1960s played Ken's other son, Peter Barlow, who still appears in the show but is played by another actor.
The only other similar example I can think of is in Jolson Sings Again, the sequel to The Jolson Story. In JSA, it has a scene where Jolson, played by Larry Parks, meets the actor who is going to play him in a proposed movie called The Jolson Story. The actor is a Larry Parks and is played by, er, Larry Parks.