The moment they were referencing was a song-and-dance bit in which O'Brien was joined ... that really was you as Deadpool," O'Brien said. "No one knows." Reynolds had a bit of fun with that ...

"Yes you were, yes you were," O'Brien confirmed.The moment they were referencing was a song-and-dance ... "Deadpool & Wolverine," and then revealed that he was the one in the Deadpool costume ...