Riverdale's K.J. Apa Mourns His On-Screen Dad Luke Perry: 'Rest in Love'

K.J. Apa is paying tribute to his TV dad, Luke Perry.

Apa, who plays Perry’s on-screen son Archie Andrews on CW’s Riverdale, shared a sweet photo of the late actor on Instagram Thursday. “Rest in love bro,” the 21-year-old star wrote.

Riverdale star Skeet Ulrich, who plays F.P. Jones, wrote, “Never forgotten… always with us,” in the comments section of Apa’s post. In addition, costars Mark Consuelos, Jordan Connor, Casey Cott and Marisol Nichols commented with multiple red heart emojis.

Perry died Monday at age 52 days after suffering a massive stroke Feb. 27. A source told PEOPLE he never regained consciousness.

Earlier on Thursday, Apa appeared to reference Perry’s death for the first time on social media by posting a screenshot of the Third Eye Blind song “The Background” to his Instagram story.

The song features lyrics that allude to moving on after the loss of a loved one, including “Everything is quiet/Since you’re not around/And I live in the numbness now/In the background.”

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The first episode of Riverdale since his passing aired Wednesday, and featured a touching tribute to the actor via a black screen that read, “In Memoriam Luke Perry 1966-2019” at the episode’s end.

Perry has been publicly mourned by friends and costars alike, including Riverdale stars Camila Mendes, Lili Reinhart, Madelaine Petsch and Molly Ringwald, who portrayed Perry’s ex-wife and Apa’s mother.

PEOPLE recently spoke to Cole Sprouse (who plays Jughead) and asked what memories of Perry he’ll hold onto forever.

“There’s a thousand things. All of us are — I don’t think there was a single bad thing I’ve ever heard said about that guy, truly. He is so loved. California is crying right now,” he said, referring to the rainy weather.

RELATED: Riverdale‘s Camila Mendes and Madelaine Petsch Remember Late Costar Luke Perry

“We were all so close to him and we all cared for him so much. He had this way of speaking that was so hyper-passionate, and he would speak, right around here to your face,” added Sprouse, 26, placing his hand a few inches from his eyes.

“He would get very close and it immediately removed all of your walls, it was this beautiful way that he had of speaking, and he would latch onto topics so passionately,” he said. “We are all still very much in the grieving process, but he seems more like the kind of guy that would want us all celebrating his funny stories rather than sitting around lamenting, and I have tremendous respect for his family who’s asked for a lot of privacy in this period. So yeah, nothing but respect.”