The Olympic gold medalist has been dating 25-year-old Megan Rossee, a bottle server at Blok nightclub in Hollywood.
The pair has been serious since January and kept their relationship under wraps while Michael was preparing to become the greatest Olympian ever at the 2012 Olympics.
“Michael and Megan have been an item since January,” a source said. “He met her in Blok nightclub - and despite advances from Paris Hilton’s ex Doug Reinhardt, she chose Michael.
“Megan thinks Michael is very funny, kind-hearted, loves hanging out with him and is just as athletic. She loves to keep in shape, so they have a lot in common.
“She was with him in Omaha, cheering him on at the Olympic trials and has been playing the part of devoted fan and girlfriend.
“Michael was desperate for her to see more of the world, so he decided that she should join him in London for the Olympics.
“He’s also hoping that eventually she quits her nightclub job to go full-time on her modeling career. He hates that she still works at Blok.
“Michael is completely besotted with Megan and now that he’s retired is even thinking of popping the question,” the source revealed.
Phelps, 27, made history at the London 2012 Olympics when he became the most decorated Olympian of all time with 22 medals.
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He also holds the all-time record for gold medals – 18 – double that of the next highest record holders.
It isn’t the first time Phelps has fallen for a cocktail waitress. In 2008, the swimming champ dated Caroline Pal, a waitress at the Palms Casino Resort’s Moon Nighclub in Las Vegas.
They met after his record-setting performance in Beijing in the same year – but there relationship soon fizzled out.