In her book, Going Off Script: How I Survived a Crazy Childhood, Cancer, and Clooney's 32 On-Screen Rejections, the Fashion Police regular, who prompted a public outcry earlier this year (15) when she poked fun at teen star Zendaya Coleman's Oscars outfit, takes aim at her former flame.
She writes, "I was being two-timed for one of the lesser Spices?"
Rancic even reveals she confronted the actor, who confessed to fooling around with Halliwell.
She adds, "(He said), 'I'm so sorry. I don't know what happened'. He had as much emotion as the customer-service representative who tells you your bags missed the flight."
Rancic claims she gave O'Connell another chance, but reveals he left her for his now-wife Rebecca Romijn at a party.
She recalls, "Little did I know he was in the VIP area, talking up Rebecca. As a prelude to feeling up Rebecca."
The TV personality lost touch with O'Connell and finally decided to confront her boyfriend at his apartment, but he refused to let her in, allegedly telling her, "Sorry, homegirl... Things change, but you take care, OK?"
Going Off Script is released this week (beg06Apr15).