The exes raised a few eyebrows on Monday when they exchanged flirty messages on Instagram.
Antonoff commented on one of Dunham’s photos after she shared an early morning shot of herself and one of her cats.
“I have two cats but only one sleeps on my face and sits on my lap while I pee,” she wrote. “The positive effect Gia Maria Carangi has had on my mental health cannot be overestimated.”
Noticing the early timestamp, the Bleachers frontman inquired about Dunham’s schedule.
“Why are you awake?” he asked.
Without missing a beat, Dunham replied, “cuz [sic] it’s the prime time to catch you on the gram, four eyes.”
Dunham, 32, and Antonoff, 33, called it quits in January after five years of dating but have remained amicable.
The former couple met in 2012 after being set up on a blind date by Antonoff’s sister Rachel and comedian Mike Birbiglia.
Days after PEOPLE confirmed Dunham and Antonoff’s split, she briefly addressed the breakup during a livestream on Instagram, saying she was still wearing a ring that Antonoff had given her.
“I’ll always wear it because love is a really cool, powerful, eternal thing,” she said. “It doesn’t have to be defined the way that we, in Western culture, define it as beginnings and ends.”
In March, Dunham was photographed out and about with an unidentified companion. She was seen wrapping her arm around him as they left dinner together.
Antonoff, meanwhile, has been linked to Carlotta Kohl; the Bleachers frontman and model sat courtside at a Knicks game in March.