Documentary filmmaker Bruce David Klein had finished shooting for the day when he was told that his subject, Liza Minnelli, wanted to see him privately. He found her sitting on the edge of her bed.

“She grabbed my hand. She started petting it and she looked up at me with those luminous, dark eyes and said, ‘Bruce, don’t put in anything phony in the movie. Don’t make me look like a phony,’” he said.

After years of arguing with his subjects that they needed to be truthful on film, Minnelli’s request was refreshing. And accepted. The result is the unvarnished documentary “Liza: A Truly Terrific Absolutely True Story.”

The film, which lands on PBS today as part of its American Masters series, offers fresh insight into an EGOT winner who overcame addiction, insecurity and the shadow of her mother — Judy Garland — to become a beloved American icon.

“We could probably have made three dozen different films on Liza’s life,” says Klein, who previously made documentaries on Meat Loaf and Carl Icahn. “It’s a big epic subject that she is.”

Klein uses old performance clips and new interviews with friends and admirers such as Ben Vereen, Mia Farrow, Chita Rivera, George Hamilton, Joel Grey, John Kander, Darren Criss and Michael Feinstein — plus revealing sit-downs with Minnelli herself.

A light bulb went on when he and Minnelli, 78, first sat down and he asked her about Fred Ebb, lyricist half of the legendary Broadway songwriting duo with Kander that wrote “Cabaret” and “Chicago.”

“Oh, Freddy,” she said. “He invented me.”

From there, Klein realized that Minnelli had leaned on five key mentors after her mother died in 1969, people who helped shape the then-raw performer — Ebb, Kay Thompson, Charles Aznavour, Bob Fosse and designer Halston.

“I think the greatest gift that these mentors gave to her was confidence — self-confidence,” says Klein.