Joined by pals Lorde, Ellie Goulding, Camila Cabello of Fifth Harmony and Jack Antonoff, the 26-year-old Grammy winner exited a bus outside the Republic Records afterparty in Los Angeles late Monday.
Although her official Grammys date was best friend Selena Gomez, Swift's boyfriend Calvin Harris, 32, was also on hand to celebrate her winning night. The powerhouse DJ was spotted entering Hyde night club with Swift's brother Austin, who came to her defense last week when West took credit for her fame in his new song "Famous."
Once inside the party, Swift and Harris' connection was on display, an onlooker tells PEOPLE. "She was sitting on his lap and they were super affectionate," says the source. "There was a mob of people around them."
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The event marks Swift and Harris' first public outing since an adorable fan crashed their dinner date in January.
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Swift debuted a new number at the afterparty, opting for a white and gold two-piece ensemble in perfect focus as she chatted up Goulding and posed for snaps with Lorde. The guest list also included Sir Paul McCartney and wife Nancy Shevell, who the onlooker says were "dancing up a storm" and hanging out with Beck after the guys were denied entry to Tyga's party.
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Despite taking a sabbatical from the limelight after wrapping up her wildly successful 1989 tour in December, Swift was center stage at the Grammys to perform "Out of the Woods" – the sixth single from her wildly successful album 1989.
Swift came full circle by winning three Grammys, including album of the year, for her first all-out pop record. In her 1989 concert film, available exclusively on Apple Music, she explained that losing album of the year for Red in 2014 inspired the reinvention Swifties have witnessed since the debut of "Shake It Off."
"I ended up going home thinking a lot about everything, thinking about where I was going, what I'd been doing, how I felt like I needed to change something," she said. "I went to bed, and I woke up at 4 in the morning, and I knew what the next album needed to be ... Everything about this new phase and this new chapter has to be different."