Dr. Dre --Take Back Your Dirty Lies ... I Don’t Have a Mistress

Dr. Dre is a loving, monogamous husband who NEVER cheated on his wife with a big booty video vixen … this according to Dre’s VERY threatening lawyers.

The Doc’s legal team fired off a cease and desist letter -- obtained by TMZ -- to TheDirty.com ... demanding it remove blog posts claiming Dre is plotting to leave his wife for model Kili Anderson.

The website even posted pics of a house they supposedly screwed in together, and a huge ring Dre allegedly gave her.

The Good Doctor says the stories are B.S. and he's demanding The Dirty immediately 86 the posts and apologize ... or else.