It was an ex-couple collision for Christie Brinkley and Peter Cook when the two had a close call at a Hamptons dance party this weekend!

Christie was hoping for a good time at the Jonas Brothers bash benefiting Ross School in East Hampton, but she ended up in uncomfortable proximity to her cheating ex -- who also attended the intimate show. As 650 fans screamed -- and Christie rocked out with son Jack -- Peter walked around with daughter Sailor.

When Christie got wind of chatter about her porny ex being in the same place -- she quickly headed for the door!

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