Simple past tense and past participle of co-star.(verb)
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Use "co-starred" in a sentence
"Cannavale, who most recently co-starred in Win Win, will recur on the upcoming season of Nurse Jackie as a tough new hospital administrator."
"On the big screen, she's co-starred in films Forgetting Sarah Marshall and Burlesque and still voices the title character of Gossip Girl."
""The polar bear will attack after this scene," Oka jokes about the intense fight scene, recalling a mysterious creature on Lost, the series that co-starred O'Quinn and also filmed in Hawaii."