Credit: Dave Hogan/Getty

This is why you should never fall in love with your costar.

Days after Us Weekly broke the news that Taylor Lautner and Lily Collins, 22, ended their one-year romance, the Abduction actors reunited to promote the thriller in London Monday.

Though they posed side-by-side, neither Lautner (in Dolce & Gabbana) nor Collins (in Versace), cracked a smile for photographers during the red carpet reunion.

And while Lautner, 19, has raved about the chemistry they once shared, audiences weren't nearly as enamored with the two actors: Abduction debuted with a disappointing $11.2 million in its opening weekend.

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What caused the young costars to split just one week before the film's L.A. premiere?

"It was a clean break that Taylor initiated," a source told Us, noting that they "barely said a word to one another" at the Abduction afterparty in L.A. September 15. See more pics of Taylor and Lily's reunion from PopSugar.

Despite his newly single status, the source added that Lautner isn't ready for another romance just yet: "He wants to be single for awhile."