Steve goes to Tony and decides to "out" himself by revealing that he's actually Captain America because he's tired of having people constantly speculating about him. Tony sets up an interview and a crew comes to the Tower and they do a live interview with a guy who isn't informed of who he's supposed to interview in advance. So he sees Steve and he's confused like "sorry, but I don't actually know who you are" and Steve basically tells him he's Captain America and they chat and Tony pops into the interview to say hi.
Think it was on AO3? If it was I forgot to bookmark it (I assume). Thanks in advance everyone!