Sean Astin is the son of Patty Duke and was adopted by her second husband John Astin.
Actually parry Duke was sure that Gomez Adams was really Sean's father. It only came out anout a year ago that Patty's 2nd husband, the one she was only married to for 2 weeks, was Sean's father.
Patty Duke still didn't believe it. Said it had to been John Auston.