"It’s taken me a couple of days to figure out how to write this," Priestley, 49, began on Instagram. "My dear friend of 29 years, Luke Perry, was one of those truly special people who really cared."
"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.," he wrote. "If you had the good fortune to know Luke, or to have ever crossed his path, I know you are sad today as well... the candle that burns twice as bright only burns for half as long... you burned oh, so brightly Luke... Goodnight Sweet Prince."
Tiffani Thiessen, who starred as Perry's manipulative love interest Valerie Malone on the series from season 5 on, also paid tribute to her former co-star.
"My heart has been weighing heavy. The loss of a man who started as my co-star but quickly became my friend. He welcomed me on my very first day of #90210 with open arms," Thiessen, 45, wrote on Instagram. "A day that was not an easy one for me. I was coming in to a show, a family really, that had been together for over 4 years. But this man took me under his wing and made me feel at home. Made me feel like I belonged in his TV family."
She continued, "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. #RIP#LukePerry #gonetoosoon."