Chris Evans Cheers on Girlfriend Jenny Slate During Her Boston Comedy Show

Chris Evans looked "proud" as he watched girlfriend Jenny Slate's comedy show, an onlooker tells PEOPLE

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Chris Evans knows what it means to be a good boyfriend. The Captain America: Civil War star cheered on girlfriend Jenny Slate during her Boston comedy show on Sunday.

Slate performed a standup set at The Sinclair in Cambridge’s Harvard Square neighborhood. An onlooker tells PEOPLE, Evans looked, “gorgeous, proud and happy” while supporting his lady. The actor was casually dressed in a grey and red baseball shirt and blue baseball cap and drove himself to the show, parking on the street, the source says.

After the performance, in which Slate shared billing with comedian Max Silvestri, Evans came out to greet about 10 of the actress’ family members, ushering them backstage.

“He was very friendly with them. It was her first time doing stand-up in front of her family even though she’s been doing it for 10 years,” an audience member tells PEOPLE, adding Slate appeared a bit nervous.

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Of the evening, Slate tweeted, “Maybe may have had one too many sips of whiskey @TheSinclair w @maxsilvestri but it was worth it&im already pumped for next Sunday!”

Evans, 35, is a native of Sudbury, Massachusetts, while Slate, 34, grew up just outside Boston in the suburb of Milton. The couple met on the set of the upcoming film Gifted, and stepped out together for the first time back in June at the premiere of The Secret Life of Pets.

Slate officially split from her husband of nearly four years, Dean Fleischer-Camp, earlier this year.