Director Steve McQueen has opened up about working with Michael K. Williams on 12 Years a Slave in light of Williams' passing.

McQueen spoke to Variety about his time with Williams, saying how Williams kept everyone's spirits lifted on set.

"I remember we were doing re-shoots, so we were very tired and we'd been shooting for a long time," he said. "Michael came on set, and he lifted everybody. Because you're shooting and tired and things are lagging, but when Michael came on set, he was so focused, so concentrated, that he gave energy to everybody. I'm not just saying it because he just passed. I remember that. His focus--we had to get to his standard. Like, 'Let's stop lying around. Let's bring it up again!' He brought everybody's focus and attention up."

"…The thing about Michael: [in] every take, he gave everything. He didn't leave anything behind," he continued. "…Unbelievable. That scene when the three of them [characters Robert, Solomon Northup and Clemens Ray] are talking about a mutiny would not have been that scene if he hadn't been in it. He wasn't in the film for that long, but he made a huge impression. I'm sorry that I didn't get a chance to work with him again, to be honest with you. He was amazing. Incredible."

Williams died Sept. 6 in his New York apartment; the cause of death has yet to be disclosed. Many of Williams' co-stars have written tributes to him, including Jonathan Majors, Courtney B. Vance, and Jurnee Smollett.

More of Williams' co-stars and friends in the industry also wrote about Williams on social media, with Bessie co-star Tika Sumpter calling Williams a "true gem" and "one of the kindest humans in all ways."