American swimsuit model Kate Upton, 21, is dating Maksim Chmerkovskiy, 33, a dancer on reality TV series Dancing With The Stars.
The couple were spotted holding hands in public at New York City's West Village neighbourhood last week and have been going on dinner dates as early as July.
A source told People magazine: "They are very serious."
But the pair, who met through a mutual friend about six months ago, started off as friends.
The source said: "Along the way, it turned into something else... It all really started just after her 21st birthday (in June). They just clicked. They have a lot of chemistry together."
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