In a statement released to Us, Jon and Jennifer said, "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 44-year-old Mad Men star and his 45-year-old Broadway beauty allegedly started dating after meeting through a mutual friends before the new millenium, in 1997.
They haven't attended an event in public together since this past January.
An anonymous source gave Us more meat for their piece, saying that the actors had "been fighting for a while" and that fighting is what led them to "finally split."