It was an unexpected sight on the NYC set of Uma Thurman‘s upcoming film, Motherhood, on Monday when the actress’ ex-husband, Ethan Hawke, paid her a surprise visit.

At first, the couple, who divorced in 2004 after six years of marriage, appeared to be in good spirits, strolling around the set together, but witnesses tell OK! that the visit did not end on a happy tone, with Ethan slamming the door of his ex’s trailer, hailing a cab and speeding off to his home.

"There’s defininitely tension there," one insider told OK! about the former couple. "They try to keep it private for the sake of the kids, but now he’s having a baby with a former nanny."

Ethan, who already has two children with Uma, announced in January that he and gal pal Ryan Shawhughes were having their first child together.

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