‘Night at the Museum’ director says the late Robin Williams was ‘struggling’ just ‘a month into the shoot’

Autopsy report showed Williams was unknowingly battling Lewy Body Dementia, his widow said

Robin Williams’ struggles were apparent while filming “Night at the Museum: Secret of the Tomb,” according to the film’s director.

Director Shawn Levy opened up about seeing Williams struggle for the upcoming documentary “Robin’s Wish,” which airs on Sept. 1.

"I would say a month into the shoot, it was clear to me – it was clear to all of us on that set – that something was going on with Robin," Levy, 52, said in a sneak peek of the documentary obtained by Entertainment Tonight.

ROBIN WILLIAMS’ DAUGHTER ZELDA ANNOUNCES SOCIAL MEDIA BREAK ON 6TH ANNIVERSARY OF HIS DEATH

In August 2014, he died from suicide at age 63 just months before “Night at the Museum: Secret of the Tomb" hit theaters.

An autopsy report showed the “Mrs. Doubtfire” star was unknowingly battling Lewy Body Dementia, his widow, Susan Schneider Wiliams, said in the “Robin’s Wish” documentary.

"We saw that Robin was struggling in a way that he hadn't before to remember lines and to combine the right words with the performance," Levy recalled.

ROBIN WILLIAMS' SON OPENS UP ABOUT LOSING HIS FATHER: 'HAVING TO SHARE HIM WITH THE WORLD WAS HARD'

Robin Williams. (Lalo Yasky/WireImage/Getty)

He added: "When Robin would call me at 10 at night, at 2 in the morning, at 4 in the morning, saying, 'Is it usable? Is any of this usable? Do I suck? What's going on?,' I would reassure him. I said, 'You are still you. I know it. The world knows it. You just need to remember that.'"

CLICK HERE TO GET THE FOX NEWS APP

"My faith in him never left, but I saw his morale crumbling," Levy concluded. "I saw a guy who wasn't himself and that was unforgivable."