Only If You Want To. (Peter Stark)
40 parts Complete Peter is actually the biological son of Tony and Pepper Stark. Though it has been kept a secret for the longest time, they plan to reveal the heir to the world when he is 16.
Extra context:
The world knows that Stark industries has an heir. everyone knows. they just don't know who it is. This is a story about the events leading up to the reveal, the reveal, and the events following.