The actress reveals she was left feeling "cheap and utterly worthless" after the incident, in which she was cornered by an unnamed celebrity in a corridor at a public event more than a decade ago.
Holden also insists she kept the attack a secret from Dennis as she feared he would confront the abuser.
She writes in her autobiography, My Life: No Holding Back, "We went to an event together and on my way back from the loo (bathroom) I was cornered by a famous comedian, who tried to kiss me and put his hands in places they shouldn't have been.
"I was scared and tried to push him away, making light of it so he would leave without causing a fuss, but he wasn't put off. As I tried to fight him off, I caught sight of our reflection in a mirror. My body went limp, and I just stood there as he groped and nuzzled me, observing myself from afar."
The actress split from Dennis in 2003 after eight years of marriage following her affair with Tv star Neil Morrissey.