Nine Year's Ago, David Sat Down with Himym Showrunners Carter Bays and Craig Thomas to Film What Would Eventually Become a Part of One of the Most Hotly Anticipated Finales in Tv History. David Signed a Non-Disclosure Agreement That Prohibited Him from Blabbing the Secret at the Time — “I Didn’t Even Tell My Mother Who the Mother Was, ” He Says — but Now He’s Free to Tell the Tale!