KJ Apa has broken his silence for the first time since Luke Perry's death.

The Riverdale star took to Instagram on Thursday (Mar. 7) to mourn his on-screen dad after he passed away from a stroke earlier this week. “Rest in Love bro,” Apa simply wrote alongside a photo of Perry enjoying a boat day.

The two played father-son duo Fred and Archie Andrews for three seasons and become extremely close outside of the show. Though they often jokingly teased each other, they knew their bond was something special. "The best thing about it for me is that we don’t have to put too much effort into the actual chemistry of it, because it just happens like that, you know? It’s easy," Apa said during one of his last TV interviews with Perry.

Apa's Riverdale castmates showed their support in the comments section of his tribute, with Skeet Ulrich, who plays F.P. Jones on the show, writing, “Never forgotten… always with us," and co-stars Mark Consuelos, Casey Cott, Marisol Nichols, Vanessa Morgan, and Madelaine Petsch commenting multiple red heart emojis.

The late actor was an important part of the cast and had close relationships with all of his co-stars, which is why showrunner Roberto Aguirre-Sacasa promised that this week's episode of Riverdale—and every episode of moving forward—would be dedicated to Perry’s memory.