"They are really good friends still and speak all the time, but their schedules just made it too difficult and it fell apart," a source told Us Weekly. "[Maksim] has a lot of respect for her, but it just wasn't working anymore."
TheDancing with the Stars professional's representative reportedly declined comment when asked about his relationship.
"She's an amazing person," the pro dancer told Us at the time.
"We have an incredible time together, and, you know, I definitely didn't see that coming and I think neither did she. We enjoy each other's company very much and like I said, she's a great girl that I never thought anything romantic like this could have happened."
The couple reportedly started off as friends when they met through a mutual friend about six months ago. Dating rumors then began to swirl in June when their relationship had reportedly taken a turn towards "serious" following a romantic dinner date for Upton's 21st birthday in New York on June 10.
Chmerkovskiy, who starred in the Ukrainian version of The Bachelor in 2011, was also previously engaged to Dancing with the Stars pro Karina Smirnoff, but the couple called it quits in September 2009.
Chmerkovskiy left Dancing with the Stars following its fifteenth season, which aired last fall. He competed on thirteen seasons without ever winning a title.