Michael Phelps Parties in London…Without Girlfriend Megan Rossee!

Olympic swimmer has "a low-key night" that seems "more like a business evening for him"

Boys will be boys!

Michael Phelps had some fun out in London Tuesday night, but girlfriend Megan Rossee was nowhere to be found.

But don't get your hopes up, ladies: The 27-year-old (now-retired) Olympian just hit up Omega House for what a witness described to E! News as "a low-key night."

"[He] was talking to the media, and then he went out into the garden," said an onlooker. "He spent a lot of time talking to Natalie Coughlin, and also [to] some Omega executives. Lots of Team G.B., including Rebecca Adlington...Michael stayed until around 11 p.m. and then went home."

"I didn't see Megan," added a witness. "It seemed more like a business evening for him."

Fair enough. We hope he and the blond stunner do get to kick back and have some fun across the pond, though!