"With great sadness, we have decided to separate, after 18 years of love and shared history," the couple announced in a joint statement yesterday.
"We will continue to be supportive of each other in every way possible moving forward."
Earlier this year, Jon Hamm completed treatment for alcohol addiction and praised Westfeldt, an actress and filmmaker, for her support. In April, they disputed reports they were breaking up. The couple were last seen together publicly in July in New York.
On 9 July 2015, we wrote...
Let's all hope and pray that this story isn't true.
It's been reported this morning that Jon Hamm and Jennifer Westfeldt are ending their relationship after 16 years. The reason? Apparently, Hamm can't commit to having children, which is reportedly what she wants.
"Jennifer realised that she and Jon don't want the same things," the source said. "So they agreed that it was time to take a step back."
The Mad Men actor had previously said he wouldn't rule out having a family, although it wasn't high on his agenda.
"I don't have a driving force to have a baby," he said. "That said, I'm in a committed relationship, and if it ever came up. I'm not ruling it out."
Other reports have linked him to Sandra Bullock. However, no official statement has been published so we're all hoping that this is all nothing but speculation.
In January, Hamm entered a 30-day-long rehabilitation programme for alcohol abuse.
"Life throws a lot at you sometimes, and you have to deal with it as much as you can," he said of rehab. "I've been very fortunate that throughout the most recent 24-hour period, I've had a lot of family and friends support me."