She said: "Lena Dunham was there, and Spike Jonze and Reese Witherspoon and Zooey Deschanel, eating pizza, talking about boys.
"We dated for a couple months and then we had a falling out," Chelsea explained.
The Florence And The Machine frontwoman turned to Swift for help after her "complicated on-off relationship" left her in "a sea of tears and confusion", she told the Sunday Times magazine.
She spoke to Swift, who is reportedly dating DJ Calvin Harris and whose former flames include One Direction star Harry Styles and American singer John Mayer, after the Met Gala - the star-studded fashion fundraiser.
"He's really sweet."I thought it was kind of amusing that I would even be with 50 Cent; I thought it was funny."And what did her famous pals think?
"My friends all loved him, my friends fell in love with him," she said.
And that includes her Hollywood BFFs Reese and Jen."They loved that I was dating him.
They were like, 'Chelsea, come on.' They were both laughing really hard at it…I mean, everyone was."So what went wrong?