Robin Williams cheered up Steven Spielberg during ‘Schindler’s List’

That’s what friends are for.

Steven Spielberg has revealed that his late pal Robin Williams called him every week to cheer him up while he was filming his 1993 Holocaust movie, “Schindler’s List.”

Spielberg’s friendship with Williams stretched back to “Hook,” the 1991 flick that Spielberg directed and featured Williams as an adult Peter Pan.

Spielberg opened up about “Schindler’s List,” and several other topics, in a wide-ranging interview in the Hollywood Reporter to talk about the 30th anniversary of the movie, which was filmed in Krakow, Poland, in 1993.

The movie, which won seven Oscars at the 66th Academy Awards in 1994 — including Best Picture and Best Director (for Spielberg) — told the story of German industrialist Oskar Schindler (Liam Neeson), who saved thousands of Jews from the Nazis during the Holocaust by employing them in his factories.

“Robin knew how hard it was for me on the movie, and once a week, every Friday, he’d call me on the phone and do comedy for me,” Spielberg said.

“Whether it was after 10 minutes or 20 minutes, when he heard me give the biggest laugh, he’d hang up on me.”

Neeson also remembered Williams’ Friday phone calls to Spielberg.

“Steven would tell us afterward the sorts of things Robin would say,” Neeson recalled. “Once he started a riff of ‘I’m not a Nazi, I’m a nutsy,’ all this sort of s – – t.”

Williams, the comedically brilliant “Mork & Mindy” star and Oscar-winning actor (“Good Will Hunting”), died by suicide in 2014 at the age of 63.

Spielberg said that shooting “Schindler’s List” took its toll on him, emotionally.

“The hard days were beyond my imagination and the easy days were never easy,” he told THR. “Everything we shot at Auschwitz with the women, when the women’s train was reassigned to Auschwitz, that was the toughest.

“Often I was a basket case, just a wreck, and [his wife] Kate [Capshaw] always sat with me, let me get it out and talked me through it, or just let me be quiet and she would be quiet,” he continued.

“We’d sit there and look at each other. Emotionally, it was the hardest thing I’ve ever done as a filmmaker.”

Spielberg said his spirits were lifted a bit when, in the middle of the “Schindler’s List” shoot, he hosted a Passover seder at a local hotel.

“All of a sudden, all the German and Austrian actors that were playing Nazis came in, put on yarmulkes and sat down next to the Israeli actors, who shared Haggadahs [Passover prayer books] with the actors who were playing their oppressors.

“I sat at the head of the table and couldn’t contain myself,” he added. “It was one of the most extraordinary, beautiful things I’d ever witnessed.”

During the interview, Spielberg also revealed for the first time that his friend and sometime-collaborator George Lucas helped mix Spielberg’s 1993 blockbuster “Jurassic Park” because Tom Pollock — who was then in charge of the feature division at the movie’s studio, Universal — balked at Spielberg working on “Jurassic Park” while he was shooting “Schindler’s List” in Eastern Europe.

“Tom Pollock . . . said, ‘I think it’s great that you’re interested in doing “Schindler’s List,” but you’ve got to finish “Jurassic Park” first,’ ” Spielberg recalled. “I was in post [production] on ‘Jurassic Park.’ I said, ‘I think I can overlap. I can do “Schindler’s List” while I’m finishing “Jurassic Park.” ‘

“I said, ‘Tom, I’m not going to abandon [“Jurassic Park”]. I’ve locked the film,’ ” Spielberg recalled. ” ‘All I have left to do is mix it, score it and correct the color.’ And he said, ‘Well, you can’t do that from Eastern Europe.’ And I said, ‘Yes I can.’ “

Spielberg said he called Lucas. “I said, ‘George, I’m in trouble. The studio’s really upset with me that I’m going to not mix ‘Jurassic Park’ and go off to Europe and make ‘Schindler’s List.’ Would you mix ‘Jurassic Park?’

“I already had his mixers working on the film,” Spielberg added, “so George said he’d take over. And he and Kathy Kennedy mixed the film.”