The pair were photographed chatting with their heads close together during the ceremony. Zellweger, 50, stunned in a silver one-sleeved gown, while Cooper, 45, was looking dapper in a tuxedo.
Zellweger — who is nominated in the best actress category for her leading role in Judy — and Cooper dated for about two years, and lived together for a few months before calling it quits in March 2011.
“I can’t say enough about her,” Cooper told Entertainment Tonight in 2010. “I just love her.”
“I [loved] coming to work. I love acting with her. I can learn so much from her,” Cooper continued, referencing the movie they worked on together, Case 39.
In January 2010, Zellweger skipped the Golden Globes to be with Cooper when his father died, PEOPLE previously reported.
Zellweger had already been nominated for three Oscars by the time she and Cooper dated, and Cooper went on to receive nominations in 2013, 2014, 2015, and 2019.
They were both up for awards on Sunday night, Zellweger for Judy and Cooper for Joker, which he helped produce.
It’s not the first time that Cooper has been friendly with an ex this awards season.
Earlier this month, the actor and ex Irina Shayk reunited at the British Vogue and Tiffany & Co. 2020 Fashion and Film Party to pose for a photo together.
The former couple were joined by British Vogue’s editor-in-chief, Edward Enninful, to whom Shayk recently opened up about her relationship with Cooper for the fashion magazine’s March 2020 cover story.
“I think in all good relationships you bring your best and your worst – it’s just the nature of a human being,” the 34-year-old supermodel said in the issue. “Two great people don’t have to make a good couple.”
“I think we’ve been very lucky to experience what we had with each other. Life without B is new ground,” she added.
The 92nd Annual Academy Awards are airing live on ABC from the Dolby Theatre in Hollywood on Feb. 9.