July 19 (UPI) -- Marc Maron said he felt the need to leave Joaquin Phoenix alone on the set of Joker while appearing on Watch What Happens Live.
Maron told host Andy Cohen Thursday about his interactions with Robert De Niro on the film and said Phoenix was dedicated to portraying the DC Comics villain.
"I met Robert De Niro and he was very nice, kind of shy, you know, not a big talker and Joaquin was pacing," Maron said.
"It was made clear to me that you just sort of leave him over there," he continued. "He was deep in."
Joker is set to arrive in theaters on Oct. 4.
Cohen asked Maron who was the all-time worst guest on his podcast, WTF, and Maron said there have only been difficult guests on the show.
"I get very diplomatic about this because, oddly, even the ones that I'm uncomfortable with, I find interesting," he said before mentioning his infamous interview with comedian Gallagher.
The interview ended early after Gallagher stormed off due to Maron asking him about homophobic jokes that he made in the past.
"I was really not, you know, indicting him," Maron said.
Maron also talked about some of the most famous guests he has interviewed on WTF , including Barack Obama, Robin Williams, Lorne Michaels, Roseanne Barr and Paul McCartney.
"When he's just alone, one-on-one, he's very shy, very thoughtful, you know seemingly somewhat sad," Maron said about interviewing the late Williams. "He didn't entertain at all, so it was just really what a sweet guy he was."
Maron additionally said that he has made up with James Franco after he shared an awkward moment with the actor on WTF.
"It was a misunderstanding. He thought I was being an [expletive]," Maron said. "I think he was being the [expletive]."