"Best of friends no matter what," Lovato, 24, captioned a sweet, smiling photo of the pair on her Instagram Story.
The pop star later shared a second pic to Snapchat of her and the That '70s Show alum, 37, basking in the sunshine.
Lovato and Valderrama broke up last June, ending their six-year relationship together.
"After almost 6 loving and wonderful years together, we have decided to end our relationship," they posted in a joint statement. "This was an incredibly difficult decision for both of us, but we have realized more than anything that we are better as best friends. We will always be supportive of one another. Thank you to everyone who has offered us kindness and support over the years."