"With great sadness, we have decided to separate, after 18 years of love and shared history. We will continue to be supportive of each other in every way possible moving forward,” the former couple released in a joint statement to People.
The Mad Men actor began dating Jennifer back in 1997 and they were considered to be one of Hollywood’s long-lasting couples.
Over the past few months, the pair faced speculation that their relationship was on the rocks.
"They've been fighting for a while, but now they're done,” a source close to Jennifer admitted to Us Magazine. “They decided to finally split. It's sad."
Despite their decision to split, Jennifer and Jon maintained a united front during some of the actor’s biggest battles – most recently his stint in rehab for alcohol addiction back in April.
The story that appeared in this week's edition of In Touch magazine is not true," Jon’s representative explained to Us Magazine. "The only gentleman Jennifer visited regularly in Connecticut was Jon, while he was in rehab. They continue to ask for the public's understanding and sensitivity during this challenging time."
The pair, who have no kids, were last spotted together on July 22 in New York at the premiere after-party for Netflix's Wet Hot American Summer: First Day of Camp.
Unlike many of Tinseltown’s famous couples, Jon and Jennifer followed Goldie Hawn and Kurt Russell’s lead, deciding not to get married.
"I don't have the marriage chip, and neither of us have the greatest examples of marriage in our families. But Jen is the love of my life, and we've already been together four times longer than my parents were married,” Jon admitted in 2010 during a sit down with Parade.
In 2012 he also voiced his love for the 45-year-old actress, “We may not have a piece of paper that says we're husband and wife, but after 10 years, Jennifer is more than just a girlfriend. What we have is much deeper and we both know that. To me, people [should] get married when they're ready to have kids, which I'm not ruling out."
It was only a year ago when the 44-year-old gushed to Peopleabout how lucky he felt to have Jennifer in his life.
"Our lives are entwined. It's a long time [together]. I'm definitely the guy that repeats his stories! Mostly it's just paying attention and keeping engaged and not succumbing to inertia or going through the motions."