The secret Stephen Sondheim wanted kept until after his death

Broadway legend Stephen Sondheim “collapsed” three times after smoking pot with friends, according to a new book — but made his pals promise to keep it a secret until after his death.

“Hairspray” composer Marc Shaiman writes in his upcoming memoir, “Never Mind the Happy: Showbiz Stories from a Sore Winner,” how he first thought Sondheim was dead when the “Company” and “Into the Woods” composer dropped to the ground.

It happened at a party at Shaiman’s house after, he writes, Patti LuPone suggested he offer Sondheim marijuana because “he loves pot.”

Sondheim readily agreed and a small group began to pass around a joint.

“But because he is Stephen Sondheim, we each keep deferentially passing the joint back to him instead of around in a circle,” Shaiman writes. “So he is easily taking in four times as much as the rest of us. Not to mention, this is when that new, stronger pot was becoming the norm, so this joint packed a punch.”

After a bit, Sondheim leaned against some crates — and suddenly dropped to the floor.

“I raced over to him,” Shaiman writes. “He sat up groggily and said, ‘Boy, that pot is really strong.’”

The “Company” composer stood up, collapsed a second time — and then a third. Shaiman recalls how Sondheim’s “eyes have rolled to the back of his head, his complexion is ashen.” And he thought: “I’ve killed Stephen Sondheim!”

In actuality, the eight-time Tony winner just needed to sleep it off. But when Shaiman checked in the next day, Sondheim said: “Thank you for calling. Just do me a favor, wait until I’m dead to tell this story.”

Sondheim passed away in 2021.

Meanwhile, Shaiman — who scored movies like “Sister Act,” “The American President,” “The Addams Family” and “Patch Adams” — turned to cocaine to keep up with his busy schedule.

“Almost every night, I would snort and snort, and when I finally knew I had to try and sleep in order to survive the next day, I would smoke a joint,” he writes. “But from smoking the joint, I would get hungry at three in the morning and eat a bagel with cream cheese and/or a bag of Chips Ahoy. I should go into the Guinness Book of World Records for being the only person who put on weight while being a cocaine addict.”

Shaiman says he was forced to shove little wads of toilet paper up his nose as he slept “because my nostrils were either running or bleeding.”

It got so bad that his housekeeper finally sat him down and said tearily: “You know I clean up the studio. I can see what’s going on, and I’m afraid for you. I want you to stop.”

He credits the housekeeper with saving his life.

Shaiman also writes about how he offended director Nora Ephron when the two worked together on 1993’s “Sleepless in Seattle.”

Visiting Ephron’s home in New York, Shaiman asked whether a black-and-white photo of an older couple was her parents.

“‘No,’ she replied acidly. ‘That. Is. A. Diane. Arbus. Photo.’”

Shaiman admits he “died a little death, since I knew Arbus was famous for photographing human oddities. Oh boy.”

Things got even frostier when an argument broke out over the movie’s music. But when they were both nominated for Academy Awards for the film , Shaiman writes, “I went very old school and sent Nora a telegram saying, ‘Well, whaddya know. See you at the Oscars!’

“No reply. She sat right behind [me] at the Oscars, but we exchanged not a word.”

Shaiman worked on “over twenty” films with director Rob Reiner, who was murdered alongside his wife last month.

He adored Reiner so much that, when introducing Reiner at a 2020 film festival, he began to weep in front of everyone.

“No matter,” Shaiman writes, “the tears spoke volumes; I was happy to let Rob and the audience know how much he meant to me.”