There are fears for the health of Playboy founder Hugh Hefner, whose weight has plummeted and who hasn’t been seen in public for months, according to a source.

“He looks like he is down to around 90 pounds and super sick. His people are really trying to keep this under wraps. You even have to sign a confidentiality agreement to go up to see him,” a source said.

Hef tweeted a photo of himself in purple silk pajamas from his “Midsummer Night’s Dream” party on Aug. 27, but he was reportedly absent from the bash, which his son Cooper instead hosted. He was also seen looking frail in May with 2016 Playmate Eugena Washington.

Hefner, 90, recently sold his Playboy Mansion for $100 million and hasn’t been seen out in LA, according to another source.

But his reps insist that “Hugh Hefner is fine. It is no secret that over the past few years he has suffered with back pain that has made it a bit more challenging for him to get around, but at 90 years of age he is enjoying his life and still very involved in the day-to-day activities of editing the magazine.”

British glamour model Carla Howe last year described how Hef was too sick to take part in his famous hedonistic parties. “Hef is so frail, he goes everywhere with a group of nurses,” she said. She added that he “never leaves home” and goes to bed at 7 p.m. after watching old movies.

However, Hef’s current wife, Crystal Hefner, 30, is more visible than ever. In July, she revealed she had to switch her breast implants after her former ones were making her sick, posting pictures of her new boobs on Instagram.

This week, Crystal, whom Hef married in 2012, posted multiple pouty pictures of herself alone in Paris, describing it as “the city of love.” There was no sign of her darling husband, who is 60 years her senior and now lives in a silk robe.

The famed LA Playboy Mansion sold in August to private equity guru Daren Metropoulos, who said Hef can live in the mansion for the rest of his life — however long that might be.