Carl was unhappy with the way he has been presented in Sullivan's book "Rivington Was Ours", and so he has sent legal letters to HarperCollins and Sullivan, reports nypost.com.
The book includes details from Gaga's early career, including how she changed her "thick, dark, raven-haired Italian mane" for a bad blonde dye job to impress her "inattentive and possessive" boyfriend Carl.
Gaga and Carl were in a relationship for three years before they parted ways in 2008.
Sullivan has described Carl as a negative influence on Gaga, asking her who she could talk to and where she could work, while he himself was "distracted by a small coterie of drunk girls".
Last year, Carl had admitted that he wasn't the ideal boyfriend.
"I was f***ing miserable, and it wasn't her fault. It was my fault for being a drunk a**hole. I would have left me, too," he had said.
Still, he has sought for legal advice over the book.
"Gaga told me herself that Luc told her early in her career, 'I hope you fail,' and that gave her the fire she needed at the time to fight for her dreams. Luc wasn't happy that I made him the villain of the piece. HarperCollins got a letter from him... he is threatening me and HarperCollins with a lawsuit," Sullivan said.
--IANS (Posted on 30-12-2013)