In Touch Exclusive:New details of Jessica Simpson’s run-in with Nick Lachey!

Jessica Simpson and Nick Lachey had managed to avoid an uncomfortable run-in since their split in 2005 — until last night in LA! Jessica — who dined with boyfriend Eric Johnson, mom Tina and a small group of pals at the Red O Restaurant — was blindsided when she realized ex-husband Nick Lachey and his girlfriend, Vanessa Minnillo, were just tables away, flaunting their affections.

A fellow diner tells In Touch the exclusive details of the star's nightmarish run-in with her ex. "They came in just minutes apart, and Jessica was told shortly after that Nick was there, too,” the eyewitness says. Jessica was dressed comfortably and wearing no makeup for what was supposed to be a relaxed dinner with her closest pals. "She had a good time with her pals, but Jessica was definitely uncomfortable knowing he was there."

Just tables away, Nick and Vanessa were sharing a bottle of red wine. While the former couple did not interact, "Vanessa must have gotten jealous,” the eyewitness speculates. “Vanessa was rubbing Nick's back, kissing his neck and ear, and running her fingers through his hair.”

The October 21 incident was only days before Jessica and Nick’s wedding anniversary — they'd tied the knot on October 26, 2002 — and despite three years of marriage, the pair didn’t make any extra efforts that evening to bury the hatchet.

But according to a source, Tina waited for Jessica to leave the restaurant and spoke briefly with her former son-in-law. "She walked up to his table and said hello," says the source. "It was friendly. He was part of her family for years.”