Confirmed: Jon Hamm Splits From Girlfriend Of 18 Years -- What Went Wrong?

It's official! After 18 years of dating -- and many breakup rumors -- Jon Hamm and Jennifer Westfeldt announced today that they have called it quits for good.

"With great sadness, we have decided to separate, after 18 years of love and shared history," the couple told PEOPLE in a joint statement. "We will continue to be supportive of each other in every way possible moving forward."

As RadarOnline.com reported, breakup rumors had swirled for weeks, with sources saying Westfeldt, 45, had been pressuring Hamm, 44, to start a family. Ultimately, an insider told Star magazine in early July, the relationship "had just run its course."

The couple were last seen together on July 22.

Before that, Westfeldt stood by Hamm throughout his stint in rehab for alcohol abuse earlier this year, as well as previous reports of his wandering eye.

Story developing.