Heidi Montag is threatening legal action against estranged husband Spencer Pratt.

The blonde beauty is furious with her former 'Hills' co-star's plans to write a book about their failed marriage, as well as giving an insight into her relationship with her mother Darlene Egelhoff.

She told gossip website TMZ: "This is exactly why I left him, right now I'm looking into my legal options."

Speaking about his book, Spencer has previously said: "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.

"This one will be totally different, I'm not holding anything back."

Yesterday (19.08.10) it was revealed the couple's divorce will be finalised on Valentine's Day (14.02.11).

Heidi served her spouse with divorce papers last month but Spencer held off signing documents confirming he had received them until August 13.

According to Californian law, Heidi will have to wait six months from that date before the divorce can be completed - meaning their marriage will not legally be over until the traditional romantic day for couples next year.

Heidi married 27-year-old Spencer in April 2009, separating 15 months later, with the 23-year-old star citing irreconcilable differences as the reason for their split.