Affleck and Shookus were together in London recently and were seen together in Manhattan on Thursday, a source who confirmed the pair were dating said to Us Weekly.
"They were together on the set of Justice League in London where Ben was filming reshoots," the source stated.
"It's more than a summer fling," a second insider shared with E! News. "They are having fun and care for each other. It's early and they are taking it slow."
Affleck's new love interest comes after the Batman star filed for divorce with Garner in April after 10 years of marriage. The pair had announced in 2015 that they were splitting. Affleck and Garner share joint legal and physical custody of their children Violet, 11, Seraphina, 8, and Samuel, 5.
In March, the 44-year-old made headlines after he entered into rehab for alcohol addiction. Following his stint, he cited his kids as an inspiration for his recovery and thanked Garner for her support.