After an afternoon of peeling back the curtain on his life with his socialite-celebrity mom Gloria Vanderbilt on the big screen, Anderson Cooper sits down at Sundance and whips out an iPhone to record me recording him. Its screen has been cracked for days, a thousand tiny tributaries crawling across the glass.

Anderson Cooper hasn’t had a chance to get it fixed.

Anderson Cooper is but a mortal man.

“I lose my wallet all the time and I break my phone all the time,” he explains with a sheepish grin. “It’s been three days but I haven’t had the time! And I’m not going to have the time for two weeks.” He pushes record: “Misquoting drives me bananas.”

The silver-haired CNN anchor, author, and journalist is in Utah to debut the upcoming HBO documentary Nothing Left Unsaid: Gloria Vanderbilt and Anderson Cooper, a feature-length portrait of his famous mother, her not-so-famous private self, and their relationship.

Directed by Academy Award nominee Liz Garbus—whose What Happened, Miss Simone? vies for Best Documentary at the Oscars next month—it’s an intimate look at the extraordinary circumstances mother and son navigated living their lives in the public eye. At the film’s Sundance Q&A, Cooper joked that his mother dated a man she described as “the Nijinsky of cunnilingus” at the ripe age of 85.

“I was actually misquoted in BuzzFeed—they said ‘ninjutsu,’ a martial art term,” he says. “I was like, the BuzzFeed writer didn’t know who Nijinsky was?”

To be fair, Nijinsky was a sort of ninja of his time, I point out.

“Well, that’s true,” he smiles. “I didn’t call in a correction or anything.”

“To realize that your mother’s love life has been far more interesting than one’s own is a weird thing to discover,” he laughs. “She’s been among the most photographed people still living today, her birth made headlines, she was involved in a horrific custody case when she was 10 years old—it was called the “Trial of the Century”—and she has had sort of epic successes and failures and triumphs and tragedies in her life,” says Cooper, who filmed his own interviews with his mother for years before starting his career in journalism. “A lot of people know the name Gloria Vanderbilt, but they don’t really know the whole story behind her, the real person that she is.”

In Nothing Left Unsaid, Cooper sits with the 91-year-old Vanderbilt to review the highlights of her unusual life as an heiress, actor, author, entrepreneur, and mother, her four marriages, and even more numerous dalliances with Hollywood’s most famous leading men. They both share the grief of losing Cooper’s father Wyatt Emory Cooper in 1978, and Cooper’s brother Carter, who committed suicide in 1988. Through Vanderbilt’s artwork, the emotional turmoil of key moments in her life are writ large.

The experience sparked an ongoing dialogue between Cooper and his mother that continued after filming wrapped, and they wrote their continued exchanges into a book, The Rainbow Comes and Goes, which will be released with the documentary.

“I realized how much like my mom I am, which I never, ever considered,” Cooper says. “We couldn’t be more different—she has never had a plan or organization in her life, and I’m completely organized and have plans. She’s very artistic and optimistic and I’m very pessimistic.”

“I consider myself a realist!” Cooper explains. “I’m not pessimistic about people. I see the good in people, but I’m a catastrophist. I plan for catastrophes, whereas my mom expects great things to happen—that the next great love is right around the corner. I expect disaster to strike.”

Cooper officially came out as gay in 2012 in longtime pal Andrew Sullivan’s blog The Dish (then a part of The Daily Beast), decades after coming out privately to friends and his mother. The film doesn’t make much fuss of it, although Cooper and Vanderbilt revisited it further in their upcoming book. Cooper explains why he came out when he did.

“At a certain point it started to feel like by not saying something, I was saying something,” he says. “It seemed like I was uncomfortable about something, which wasn’t the case. I was leading a very open gay life with my partner in New York, we’d go to gay bars…so I wrote out a letter, like a public statement, and I had it published on The Daily Beast.”

“I was actually in Africa when it was published. The day it went online I was in Botswana in a remote camp that had no Internet or phone connection, and I remember I’d forgotten to tell my mom that it was going to be published. So she read it in The New York Times and I couldn’t reach her for three days. When I finally got to a phone she said, ‘Oh, I saw that thing! I didn’t know you were going to do that!”

He mentions Olympic medalist Gus Kenworthy, a freestyle skier who came out last year. “It’s a remarkable thing that, at the height of his career, he took this risk in a sport in which there is nobody else who is openly gay. I think there is still certainly a need for people to be open to the extent that they can be.”

“I’m certainly not one to preach to anybody about what they should do with their lives, but I do think visibility is important,” he continues. “I understand that people were critical of me for not doing it sooner, and I understand the desire to have people who are visible in the public sphere, but I think we do what we can.”

Cooper considers the empathetic streak that colors his work and earned him a label as an “emo journalist.”

“I thought it meant Emo Phillips the first time I heard it,” he smiles. “I find that term interesting because on cable news on a nightly basis you see people angry and yelling, and that’s emotional. But anyone who expresses a genuine emotion of empathy or pathos or care for another human being, that’s ‘emo.’ I think that says more about where TV is at. That was during Katrina, a particularly extraordinary time in our country. I think to not have an emotional response was virtually impossible.”

“It’s also interesting because I’m one of the least emotional people that I know,” he adds. “I press down all my emotions, deep down inside.”

I ask if it’s important to him to take politicians to task, as he’s done publicly with Donald Trump in the run-up to November’s election.

“I think it’s just important to be factually correct,” he emphasizes. “So if someone’s saying something that’s not factually correct, whether it’s Donald Trump or Hillary Clinton or any candidate, I think it’s our job to point that out.”

“And you can point that out until you’re blue in the face and some people will listen, some people won’t, and that’s fine. But I think my job is just to try to be as accurate as possible and as fair as possible. I don’t argue with people about opinion because everybody has the right to their opinion. But facts matter, and it’s important that viewers have facts so they can make up their own mind.”

He describes the contemporary media landscape as “the golden age of information,” but says there’s still considerable work to do to ensure that the voices telling the news reflect the America they’re informing.

“There’s not enough diversity, but there’s greater diversity than ever before,” Cooper says. “I’m talking about racial diversity, I’m talking about gender, sexuality, economic, geographic, all sorts of diversity, all of which is important to have in a newsroom. And there are more options than ever before. That’s all to the good. If anything, I think there’s too much information that it’s hard to figure out where the information is coming from, who’s actually behind it, what is their agenda, what is their bias if they have a bias. But I think diversity is important. The more diverse we are in our media, the richer we all are.”

With that, Cooper bids goodbye. The next day he’ll depart the snowy mountains of Sundance for Iowa ahead of the Republican and Democratic caucuses. “Back to politics,” he says with a grin.