The "Younger" star, 28, and the former NHL player were spotted kissing after they spent the day with their 4-year-old son, Luca, reported US magazine.
As Duff got into her car to leave, Comire, 35, leaned in for a goodbye kiss.
The couple announced their split two years back, but have kept their differences aside to spend a lot of time together to co-parent.
In March, the former Disney star shared photos of the pair celebrating Luca's 4th birthday and hanging out at Duff's mom's house.