The moviemaker, Girls' executive producer, picked up a Peabody Award for Dunham's comedy series at the 72nd annual prizegiving, which honours the best in Tv.
Speaking to reporters at the event, Apatow confessed he let down his protegee Dunham when he forgot her big day.
He tells the New York Post gossip column Page Six, "I found out from (my daughter) Maude, who saw it on (news show) Entertainment Tonight. I got her no presents, just a late-in-the-day email. I was not a good friend.
"I wasn't invited to a party. Maybe there was a party, and I didn't get to go?"
Winners of the Peabody Awards, which were first announced in March (13), also included hit dramas Louie, Game Change, Switched at Birth, and Southland.