A former news anchor has accused actor Kevin Spacey of sexually assaulting her 18-year-old son, leaving him traumatised.

In a tearful press conference, Heather Unruh said her star-struck son had been at a bar in Nantucket in July 2016 with the actor, who she claimed had bought him drink after drink.

Spacey stuck his hand inside my son’s pants and grabbed his genitals, she claimed.

Spacey is yet to comment on the recent allegation.

It came just a week after actor Anthony Rapp accused the star of sexually assaulting him when he was 14.

Since then, other allegations have surfaced and the Oscar-winning star said he is seeking evaluation and treatment.

Ms Unruh claimed her shocked son had attempted to remove Mr Spacey’s hand but the violation had continued.

There was no consent, she said.

The teenager had lied to Mr Spacey about his age, she said, but whether he was over 21 or not, Kevin Spacey had no right to sexually assault him.

According to the allegations, the assault continued until Mr Spacey went to the toilet and a concerned woman nearby approached to ask if the teenager was okay.

On the bystander’s advice the teenager fled to his grandmother’s home, where he and his sister called their mother. The family are now appealing for the unknown woman to contact them.

Ms Unruh said embarrassment and fear meant her son did not inform authorities at the time, but that he had filed a police report following the tide of allegations against Harvey Weinstein last month.

She said he had been harmed by the incident.

Nothing could have prepared my son for how that sexual assault would make him feel as a man, she said.

While he has tried his best to deal with it, it’s always there and continues to bother him.

Spacey has said he was beyond horrified by Rapp’s previous claim of assault.

I honestly do not remember the encounter, it would have been over 30 years ago, he said in a Twitter statement.

But if I did behave then as he describes, I owe him the sincerest apology for what would have been deeply inappropriate drunken behaviour and I am sorry for the feelings he describes having carried with him all those years.

He added in the revelation had encouraged him to address other things about his life and revealed that he now chooses to live as a gay man.

(c) Sky News 2017: Kevin Spacey: Journalist claims actor sexually assaulted teen son