Original Grey’s Anatomy castmember T.R. Knight is reacting to the untimely death of his fellow costar, Eric Dane.

“Eric, your generosity and humor will always be a guide, your courage and honesty, a beacon,” Knight, 52, wrote via Instagram on Saturday, February 21, alongside a photo of the former Shondaland stars. In the pic, Knight can be seen fixing Dane’s bowtie while the late actor smiles.

“My heart is a part of the vast circle that surrounds you and loves you,” Knight continued in the caption.

Us Weekly confirmed on Thursday, February 19, that the former Euphoria star died after a battle with ALS. He was 53.

Eric Dane Through the Years: From ‘Grey’s Anatomy’ Fame to ALS Health Battle

“With heavy hearts, we share that Eric Dane passed on Thursday afternoon following a courageous battle with ALS,” a statement from Dane’s family read at the time. “He spent his final days surrounded by dear friends, his devoted wife, and his two beautiful daughters, Billie and Georgia, who were the center of his world.” (Dane shared his two children with his wife, Rebecca Gayheart.)

The statement continued, “Throughout his journey with ALS, Eric became a passionate advocate for awareness and research, determined to make a difference for others facing the same fight. He will be deeply missed, and lovingly remembered always. Eric adored his fans and is forever grateful for the outpouring of love and support he’s received. The family has asked for privacy as they navigate this impossible time.”

Knight, who played George O’Malley on the hit ABC drama from its inaugural 2005 season to 2009, is just one of many of Dane’s former Grey’s Anatomy castmates to offer their love and condolences in the wake of his death. (Dane joined the show in February 2006 as Dr. Mark Sloan. The actor died on the 20th anniversary of his first appearance on the program.)

“The last 48 hours have been devastating,” Chyler Leigh, who played Dane’s love interest Lexi on Grey’s Anatomy, told E! News in a Saturday statement. “I never thought I would be using the term ‘had or was,’ but here we are. And I hate it. Eric had a heart of gold. His humor and, especially, his laugh was infectious. He was a deeply intelligent man who could carry a philosophical conversation for hours even while we were on set. He was an amazing father and loved his girls FIERCELY. Incredibly passionate about his work and the causes he kept close to his heart.”

Dane’s onscreen best friend-turned-enemy-turned-best friend again, Patrick Dempsey, also praised the late actor in the wake of his untimely death.

Eric Dane’s Most Memorable Roles Before His Death: From ‘Grey’s Anatomy’ to ‘Euphoria’

“I just woke up this morning and it was very sad to read the news. It’s hard to put into words. I feel really so sad for his children,” Dempsey, 60, said on The Chris Evans Breakfast Show on Virgin Radio U.K. on Friday, February 20. “I was corresponding with him, we were texting, so I spoke to him about a week ago, and some friends of ours went in to see him and he was really starting to lose his ability to speak. He was bedridden and it was very hard for him to swallow, so the quality of his life was deteriorating so rapidly.”

Dempsey continued, “He was the funniest man — he was such a joy to work with, and I want to just remember him in that spirit, because any time he was on set, he brought so much fun to it. He had a great sense of humor. He was easy to work with. We got along instantly. First scene was him, you know, in all his glory, coming out of the bathroom with the towel on, looking amazing, making you feel completely out of shape and insignificant.”