9:50 AM PT -- Luke's "Riverdale" costar, Camila Mendes, has also shared a touching tribute, saying ... "he took care of us all. an authentic man who took pleasure in offering us his guidance and wisdom. his presence was healing; he had the ability to make you feel comfortable and at ease within seconds of seeing him."

She added ... "we lost a dear friend. my heart hurts for his family and anybody who had the pleasure of knowing him. rest in peace, luke. although you’re no longer around to wrap me in the warmth of your hug, i can still remember what it felt like. whenever i think of you, i will remember that feeling."

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9:15 AM PT -- Another one of Luke's former '90210' costars, Tiffani Thiessen, has shared a tribute to him as well. She says he welcomed her with open arms when she joined the well-established show, took her under his wing and made her feel like part of his TV family.

Tiffani adds ... "He was sincere, sweet, warm, kind, professional and funny as all heck. And most of all, the definition of a gentleman. Luke, our world has a hole in it now that you aren’t here. But heaven definitely gained you as an angel."

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Jason Priestley just broke his silence on the passing of Luke Perry ... with a touching tribute to his late friend and former costar.

The "Beverly Hills, 90210" star penned an emotional tribute on Instagram Thursday ... saying Luke was taken from this world far too soon. He wrote, "It's taken me a couple of days to figure out how to write this ... My dear friend of 29 years, Luke Perry, was one of those truly special people who really cared."

He added, "Luke was not only a star, he was an incredibly bright light that was extinguished far too soon... and that is why I, and so many others, are in so much pain today... if you had the good fortune to know Luke, or to have ever crossed his path, I know you are sad today as well."

Jason's thoughtful tribute came a few days after Luke died from a massive stroke he'd suffered 5 days earlier. Their characters -- Brandon Walsh and Dylan McKay -- were close friends on the '90s teen drama, and that friendship continued offscreen.

Jason's tribute comes on the heels of "Riverdale" also honoring Luke after resuming production. Wednesday night's episode -- the first to air since Luke's passing -- closed with an "In Memoriam" tribute.

As you know ... "Riverdale" has dedicated the rest of the show to Luke, who played Archie's dad on the hit CW series. The show's executive producer referred to Luke as "Our heart, always."

Jason echoed that sentiment ... "The candle that burns twice as bright only burns for half as long.... you burned oh, so brightly Luke... Goodnight Sweet Prince."