The unlikely trio performed 'Heartbeats' by The Knife while standing in the corridor of the London house, with Ed strumming away on his guitar by the staircase.
Taylor posted a video of the sing-along on her Instagram page. She said: "Me, Ed, Cara. Singing songs in the US ambassador's house. What is life."
Model Cara was filmed singing along softly to the words, as she let Ed and Taylor take the main vocals. Perhaps these three could start their own band?!
In another photo, Cara and Taylor are posing in front of a large portrait painting hanging on the wall. Taylor said: "Just trying to be like George Washington."
As well as treating fans to guest appearances on her current 'RED' tour, and during her string of London dates this week, Taylor performed with British sensation Sam Smith, The Script frontman Danny O'Donoghue and Ed on consecutive nights.
Taylor will be performing in Berlin tonight, before returning back to London for two more shows next week.
What do you think of Taylor, Cara and Ed's performance? Tell us below, as the best comment from across the website each week wins £50!
Got an iPad or iPhone? Reveal Mag has been especially designed to fit!