Chris Sawyer, 27, said he heard the couple enter his London apartment through a door that had been left open by a neighbor in the early hours Saturday and the pair went into the bedroom of his roommate, Sean Thorne, 24, who was not home, and had sex, The Sun reported Tuesday.
Sawyer said he called Thorne before taking pictures of the incident and posting updates about the rendezvous on Twitter. He said he took video of the embarrassed couple exiting Thorne's room.
Thorne said he has thrown away his bed sheets. He said the couple did not take all of their belongings when they left.
"I've got his red trousers as he took mine by mistake. I think it's quite funny now," he said.
The roommates said the girl, who had been attending a party at a neighbor's apartment prior to the incident, sent some friends to the apartment later to collect her hot pants and other items.