Hamm walked the red carpet at the Cort Theatre before reportedly heading inside to join Shookus for a production of Derren Brown: Secret.
"They sat together on the aisle and looked like they were having a great time," a source told People. "It very much felt like they were on a date. When they were talking to one another, they locked eyes and were smiling the whole time."
A source tells ET Lindsay Shookus and Jon Hamm have been "friends for years." The Man Men alum has hosted SNL three times -- and has made multiple guest appearances -- over the last 11 years.
Meanwhile, the Broadway outing with Hamm comes a little more than five months since Shookus and Affleck called it quits for the second time.
The pair previously dated for over a year before splitting up shortly before Affleck entered rehab in August 2018. Following Affleck's brief romance with model Shauna Sexton, the Justice League star reconciled with Shookus in February.
The pair seemed to be going strong again before their schedules got in the way of their relationship, and the pair called things off once again.
"The distance was definitely a huge factor in their breakup," a source told ET at the time. "They both have a lot of love for each other but ultimately they realized it was not going to work."
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Reporting by Carolyn Greenspan.