"The Hills" villain, 26, tells UsMagazine.com exclusively that he is penning a tell-all about his relationship with ex Heidi Montag, including new details about her tormented relationship with her mother, Darlene Egelhoff.
"My last book, How to be Famous, didn't make the New York Times best-seller list because it was in the self-help section," Pratt tells Us. "This one is going to be totally different. I'm not holding anything back."
Montag told TMZ that she is looking into her legal options to stop this book from happening.
In July, Montag filed for divorce after one year of marriage, citing irreconcilable differences. Their divorce is expected to be finalized on Valentine's Day of next year.