The former teen idol icon died late last month at the age of 67 from organ failure, only seven months after it was announced that he was battling dementia.
Now Samantha Fox says he "stormed" into the bathroom of a restaurant where they were filming and aggressively started to grope her.
"His hands were all over me. I shouted: ‘Get off me, David!’ in an attempt to stop him. But instead, he just stuck his tongue into my mouth and shoved a hand under my skirt, while the other kept a firm grip on one of my breasts," she told the Daily Star.
She added: “I reacted quickly and instinctively by bringing my knee upwards, striking him right in the balls… then I elbowed him in the face.”
Fox also says that Cassidy had an erection when they were being photographed together.
"Whenever he pressed himself against me, I could clearly feel his dick," she stated.

David Cassidy, who died last month, first came to the world's attention as the star of the smash hit TV show The Partridge Family, which aired from 1970-74.
The show gave him an audience for his music and his first major single 'I think I Love You' hit number one, selling five million copies.
At one point, his fan club had more members than Elvis or The Beatles.
His clean-cut image changed when he gave an interview to Rolling Stones magazine, posing naked on the cover and confessing to experimenting with drugs.
Cassidy hit the headlines in later life when he was arrested on numerous occasions for drink-driving charges. He bravely revealed that he was suffering from alcoholism.
But his greatest battle was to follow earlier this year when he was diagnosed with dementia.

His family released a statement after his death last month, stating: "A statement from his family said: "David died surrounded by those he loved, with joy in his heart and free from the pain that had gripped him for so long. Thank you for the abundance and support you have shown him these many years."
The star's nephew Jack Cassidy, a singer himself, took to Twitter to pay his respect. "My uncle David Cassidy has sadly passed away tonight... & in the process of mourning I can't help but thank God for the joy that he brought to countless millions of people! I don't think I'm alone in saying that we will all miss him. God Speed!" he wrote

My uncle David Cassidy has sadly passed away tonight... & in the process of mourning I can't help but thank God for the joy that he brought to countless millions of people! I don't think I'm alone in saying that we will all miss him. God Speed!

— Jack Cassidy (@jackgcassidy) November 22, 2017