Lamar and Khloe Livin' in Sin!

TMZ has learned Lamar Odom and Khloe Kardashian are not legally married ... and they won't be until a prenup is signed.



We've learned two high-powered family law attorneys are already squaring off, trying to hash out the prenup Odom wants as a condition to marriage. Neal Hersh is doing his bidding, while Lisa Meyer is repping Khloe. We're told the negotiations -- which began last Friday -- are already contentious.

Our sources say the couple will tie the knot -- legally -- once the prenup is inked.