updated 12/20/2013 AT 4:00 PM ET
•originally published 12/20/2013 AT 5:05 PM ET
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.
“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.