Jon Hamm & Jennifer Westfeldt Spark Rumors They're Back Together

New photos have us wondering if Jon Hamm and Jennifer Westfeldt are back on.

Following the estranged couple's announcement in September that they were separating after 18 years together, the Daily Mailgot exclusive photos of Jon, 44, and Jennifer, 45, as they arrived at an event honoring the late director Mike Nichols on Sunday night in New York City.

WATCH: Why Jon Hamm and Jennifer Westfeldt Split After 18 Years

The two walked arm-in-arm as they strolled into the IAC building in Manhattan where Nichols' widow Diane Sawyer hosted.

This marked the first time the couple has been seen in public together since the split announcement, but they have broken up and reconciled before, making it seem more plausible that they could settle their differences again.

In March, Jon completed treatment in a rehab facility, where he sought help in battling an alcohol addiction. During that time, Jennifer stood by side.

WATCH: Jon Hamm Breaks Silence Post-Rehab, Talks 'Mad Men' Movie Possibility

"With the support of his longtime partner Jennifer Westfeldt, Jon Hamm recently completed treatment for his struggle with alcohol addiction," his rep told ET about his 30-day stay.

Jon and Hamm first began dating in 1997, but have never married and have no children.