AceShowbiz - Taylor Swift surprised her fans, famously known as Swifties, with a special guest performer at her recent "Eras Tour" show. The "All Too Well" hitmaker and Gracie Abrams offered concertgoers a performance of "us.".

On Sunday, June 23, the 34-year-old superstar took the stage at Wembley Stadium in London, the United Kingdom to entertain her fans as a part of her ongoing world tour. At one point during the show, she told the packed audience about her surprise guest, who joined her to deliver their collaborative track that was released on Friday, June 21.

Standing alone onstage, Taylor stated, "We're celebrating eras of music and I'm gonna challenge myself to sing as many eras of music as possible, and it's been one of my favorite parts of the tour. If you know the words to this one, you get extra credit points because it's only been out for, like, two days."

Noting that the song is "technically not one that's mine at all, it's my friend Gracie's," Taylor went on to gush, "When I tell you I just love this girl so much ... but when you write with someone it's like you see the whole thing [and] all the artistry, you see who this person is really and writing with her, she's like so bada**."

"Like, that's a writer," the "Shake It Off" songstress continued, before Gracie stepped on the stage. "I was telling her tonight that I would gauge the excitement level for the song. I'm gonna play the song 'Us.' So, Gracie's album 'Secret of Us' just came out. I love you so much. ... We had cosmos and dinner and then we came home and opened wine and we were just talking about life."

For the performance, Taylor showed her skills in playing guitar while Gracie played the piano. Together, they sang, "I know you know/ It felt like somethin' old/ It felt like somethin' holy, like souls bleedin', so/ It fеlt like what I've known/ You're twеnty-nine years old/ So how can you be cold when I open my home?"