The former couple, which has remained close since parting ways three years ago, reunited over the weekend as Demi popped up during the actor's video streaming session and exchanged sweet compliments with Wilmer.
"You look awesome, girl!" the "That '70s Show" star told Demi, who replied, "Thank you! So do you."
They then broke out into a rendition of 2000 hit "Who Let the Dogs Out" by the Baha Men, before the singer/actress made her exit, having made tentative plans to hang out with Wilmer again after work on Wednesday.
"See you, angel. Love you," he said, as he bid farewell.
The sweet Instagram Live appearance comes nine months after Demi suffered a near-fatal drug overdose last summer (2018).
Wilmer was among the first of her close friends to visit the 26-year-old in hospital and lend his support as she continued her recovery in rehab, and earlier this month, Demi's mother, Dianna De La Garza, admitted she was quietly hoping the "Sorry Not Sorry" hitmaker would get back together with the 39-year-old actor.
"If Demi came up and said they were getting back together, I would not have a problem with that at all," she told Us Weekly. "But at the same time, those are her decisions...."
"Wilmer will always have a very special place in our hearts and in the family and that will never change, for any of us."
Her mum's wish may still come true - Demi has been single since splitting from fashion designer Henry Levi in early March after a few months of dating.
Meanwhile, she and Wilmer dated on and off for six years prior to calling it quits for good back in 2016.