Joaquin Phoenix says he regrets his infamous interview with David Letterman, in which he remained in character for the entire, awkward conversation.

The actor was promoting the mockumentary 'I'm Still Here' when he delivered one of the strangest interviews ever recorded for late night television.

Joker star Joaquin Phoenix recently returned to The Late Show after a whopping 15 years — but something else also happened: he apologized for his infamous David Letterman interview from 2009 that took place on the show before Letterman turned the reins over to Stephen Colbert.