Michael Phelps' mystery girlfriend is model Megan Rossee

The mystery woman Michael Phelps was spotted leaving with at a London party at 4 a.m. Sunday night has been revealed.  The blond-haired beauty is model Megan Rossee and the two have been quietly dating for five months according to the website Hollyscoop.

The Olympic swimmer was spotted leaving a London club after celebrating his 4x100 gold medal Sunday night with his teammates.  Phelps exited the party with a bunch of gold medals over his neck and the unidentified Rossee on his arm and jumped into a waiting SUV— leading to a lot of speculation about who she was.

Phelps is notoriously quiet about his love life but it appears Rossee couldn't keep it a secret any longer.  She went public with their relationship by posting photos of them on Instagram.  As usual,  he was still holding a bundle of medals.

The couple have reportedly been an item for over five months.

"She and Phelps started dating in January (2012) and things started to heat up just prior to the Olympics," a source told Hollyscoop.

The 5'9" former cocktail waitress— who describes herself on Facebook as a "model and actress"— has posted sexy photos of herself (with her friends) on Twitter and her nickname for the human dolphin is "Bear."

Phelps flew Rossee to London for the Olympics and now she can help lug the hardware back.

Michael Phelps leaves party with mystery woman and gold medals

Michael Phelps continued to collect gold even after his 2012 Olympics was over.  The swimmer was seen leaving a "boozy" London party with a golden-haired mystery woman after celebrating at the exclusive House of St. Barnabas-in-Soho, according to The New York Post.

Phelps celebrated his 4x100 meter relay victory with his teammates and he kept the party going by getting into a waiting SUV at around 4 a.m. with his blue-eyed beauty with the red, white and blue fingernails.

The couple reportedly smuggled a couple of bottles of Stella Artois into their ride while a triumphant Phelps showed off some of his gold medals for the cameras.

The leggy-woman was a little more camera-shy and hid from the photographers but, once inside the car, she smiled seductively.

Even though the 27-year old Phelps' Olympic career is over, the swimmer said he still woke up at his usual 6 a.m. training time.

"I only had three or four hours of sleep last night, then I woke up and couldn't fall back to sleep," he said.

It sounds like Phelps is having a hard time with retirement already and he still has to wait 38 more years for social security benefits.

"It's kinda weird. It's very strange, the first day of not having to swim and never having it again," he said.  "I'm not sure right now how I feel.  It's really confusing."

Phelps said he plans to spend his first day of retirement with his biggest fan, his mother Debbie, and would not be going near a pool except to watch the Olympics and world championships.

The competitive part of my career is over, but it doesn't mean my involvement with swimming is over," he said.  "I'm still going to be involved, but looking at it from the outside."

I'm sure there will be other mystery woman coming in and out of Phelps' new life of leisure. Wearing a bundle of gold medals around your neck can't hurt.