Mohamed Hadid to Lisa Vanderpump: You're Dead To Me!!!

Lisa Vanderpump's calling BS on Mohamed Hadid's kids suffering from Lyme disease, and her accusation is having major repercussions for the 'Real Housewives' shoots.

Sources tell TMZ Lisa and Mohamed's 20 year friendship came to an abrupt end when Vanderpump, for the umpteenth time, asked about his kids, Bella and Anwar, and their Lyme disease. We're told Hadid was embarrassed because Lisa asked while taping at dinner with friends.

Sources close to the situation tell us Hadid will be cordial during shoots, but ANY attempt to renew the friendship -- even for the show -- is out of the question, as far as he's concerned.

We're told Lisa's husband, Ken, even tried to patch things up, but Hadid's not budging ... and hasn't even been to any of Lisa's 3 restaurants since the drama.

Lucky for him it's a big city.