Robin Williams' Mork & Mindy co-star has accused him of groping and flashing her on the set.

The accuser - Pam Dawber - claims he grabbed her breasts and backside, and also flashed her in a new biography of the late actor by New York Times journalist Dave Itzkoff.

“I had the grossest things done to me by him,” says Dawber, who starred as Mindy. “And I never took offence. I mean I was flashed, humped, bumped, grabbed."

However the now 65-year-old actress writes it off as playful behaviour.

"I think he probably did it to a lot of people … but it was so much fun," she adds.

In addition to groping and exposing himself to her, Williams also wrestled her and showed up to set completely nude.

In one instance he "goosed" an elderly woman portraying Mindy's grandmother by putting a cane in-between her bottom.

Itzkoff's biography of Williams is due out in May and sections were reproduced by the Daily Mail.

“If you put it on paper you would be appalled,” says Dawber. “But somehow he had this guileless little thing that he would do – those sparkly eyes."

She continues, "He’d look at you, really playful, like a puppy, all of a sudden. And then he’d grab your tits and then run away."

She attributes him getting away with it to because "it was the '70s."

The director of Mork & Mindy Howard Storm says that "it was just Robin being Robin” and that he groped his co-star because he was "bored."

Storm added, "He’d be doing a paragraph and in the middle of it he would just turn and grab her ass. Or grab a breast. And we’d start again. I’d say, ‘Robin, there’s nothing in the script that says you grab Pam’s ass.’ And he’d say: ‘Oh, OK.'"

Mork & Mindy producer Garry Marshall said Williams' "life aim was to make Pam Dawber blush."

The show aired from 1978 to 1982 and chronicled the story of an alien [Williams] who lived with Mindy [Dawber] in Boulder, Colorado.

It helped launch Williams' Hollywood career, as he went on to star in Mrs. Doubtfire, Dead Poets' Society, Good Will Hunting and more.

In 2014, Williams killed himself following a history of drug addiction, depression and mental health issues.

Regardless of Williams' behaviour, Dawber described their relationship as sibling-like and said the late actor had a "gigantic heart."

The Independent reached out to Williams' estate for comment, but has not yet heard back.