Tom Hollander Says He Still Hasn’t 'Really Mourned' Feud Costar Treat Williams: 'It’s Very Tragic' (Exclusive)

When Feud: Capote Vs. The Swans premieres Wednesday night, viewers will see Treat Williams in his last major role.

The actor spent some of the final days before his fatal motorcycle accident in June on set of the new FX series that tells the story of Truman Capote’s fallout with Manhattan’s socialites, who the author called his “swans,” in the aftermath of releasing his salacious "La Côte Basque, 1965" story.

Williams, who died at age 71, portrays CBS co-founder Bill Paley, the powerful husband of Capote’s former confidante Babe Paley (Naomi Watts).

“It's very, very tragic and it's quite difficult for us to talk about because he was right there just now,” Tom Hollander, who portrays Capote in Feud, tells PEOPLE of Williams' death. “We haven't really mourned him. We were just getting to know him. He was a very, very sweet spirit. He was the most positive up, glass-half-full enthusiast.”

The British actor, 56, believes Williams “was so happy to be there” working on Feud and considered him “so generous and talkative.”

Watts, also an executive producer Capote Vs. The Swans, tells PEOPLE she thinks Williams “gave it his absolute all” when it came to playing Bill Paley.

“He was delighted every day with these incredible scenes,” the mom of two, 55, continues. “He talked about it, ‘I cannot believe I've got such good material.’ And I think we all felt like that, even some of those scenes where he was behaving horribly — the character, not Treat!”

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Babe had been dying of lung cancer when Esquire published "La Côte Basque, 1965," in which Capote outed an affair Bill had been having with the wife of a New York governor. Despite his alleged philandering, Bill continued to care for his wife in her dying days, a performance Williams nailed according to Watts.

“The times where Babe is at the end of her life, he had emotion that was so easily accessible,” she says. “And I think it was a lot to do with being at this point in his life where he was just so grateful. We're all completely heartbroken by it and devastated that he's not going to see his wonderful, wonderful work up there.”

Feud director Gus Van Sant actually met Williams decades before they worked together on the Ryan Murphy-helmed limited series.

“Treat and I had met one time at an audition a while ago, I think in the ‘90s,” Van Sant, 71, tells PEOPLE. “But besides that, we hadn't seen each other since then. And he grew up in the ‘60s next door to where I grew up in Darien, Connecticut. He was from Rowayton, Connecticut. So there was a lot of people that he was related to that our family knew that I knew. And it was fun to just talk to him about the ‘60s, because we're the same age and all the things that happened in our community we both experienced.”

Van Sant found Williams to be a “really a fun person to talk to.”

“He was often telling a long story to somebody on the set to the point where the first AD had to quiet him down,” he shares. “It was really tragic to have him leave us.”

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Feud: Capote Vs. The Swans premieres Wednesday at 10 p.m. ET on FX.