The 62-year-old model and her boyfriend since last September, 64-year-old musician John Mellencamp, have broken up, their rep confirmed on Tuesday.
"Both the mileage between their homes and their heavy career demands interfered with their ability to maintain the relationship," a rep for both Brinkley and Mellencamp tells ET. "They vowed to remain best of friends."
The two appeared happy during their latest sighting together in May in Los Angeles, when they held hands during a dinner date at celeb hot spot Craig's.
"I'm leery of discussing my relationship because I don't want to jinx it," Brinkley, who's been divorced four times, admitted last November during an appearance on Howard Stern's SiriusXM show when asked about possibly marrying Mellencamp. "And I feel like I was so dragged through the press that I [don't want that again]."
...But perhaps Brinkley's next beau will be a younger man?
"It seems like during this period that most of the guys are like 38, 39, 42, like that sort of age group," the mother of three told ET about her dating life in January 2014. "It's funny because I think that at that age they have nothing to prove. They're very confident and do just what they want to do. [With] men my age I feel quite invisible to them."