It was impressive enough that Taylor Swift booked a four-night run of sellout performances at L.A.’s Staples Center. Then she went and added surprise cameos from Justin Bieber and Jason Mraz, who each popped up for unannounced duets. Sunday night marked the end of Taylor’s Staples residency, and she had yet another surprise special guest for her fans: Ellen DeGeneres.

“I was looking for the ladies room. I am so sorry,” quipped DeGeneres after appearing onstage.

“This has been happening quite a bit,” Swift joked. “People are just going about their daily lives and they end up on our stage. It happened a lot this week.”

DeGeneres then proceeded to sit in on ‘Our Song,’ executing an impressive in-song switch from the maracas to the triangle before bidding the crowd farewell and sharing the news with her Twitter followers: “Just got off the stage with @TaylorSwift13 at Staples Center. Our song is now ‘Our Song.’”

[via PopCrush]