Kate Upton, 21, and Maksim Chmerkovskiy, 33 – who were said to be "very serious" as recently as the end of September when they were photographed holding hands – have called it quits.
"They've been done for a while," a source tells PEOPLE, of the hot-bodied pair, who met through a mutual friend at the beginning of this year.
The Sports Illustrated cover girl and former Dancing with the Stars pro solidified their romance during an intimate dinner at Scalinatella in New York City to celebrate Upton's 21st birthday in June.
"They just clicked," a source told PEOPLE of the pair. "They have a lot of chemistry together. They get along great. They have a lot of fun together."
Chmerkovskiy has raved about Upton, telling PEOPLE last month: "She is extremely intelligent. We talk about everything including politics. She got everything pretty much herself and I respect that. I love how she can go from being girly to being a businesswoman in the snap of a finger."
A rep for Chmerkovskiy would not comment on his personal life.