Locklear / Sambora Divorce -- Fight Over Custody?

TMZ has obtained Richie Sambora's legal response to Heather Locklear's divorce petition, and it's a sign of trouble.

Sambora is asking the court for joint physical custody of their eight-year-old daughter, Ava. In her petition, Locklear asked for sole physical custody.

Sambora claims the couple separated the day after Christmas last year. He also confirms what Locklear claimed -- that the couple signed a prenup on December 14, 1994. They married the next day.