The actor, who is perhaps best known for playing Roy Harper in the DC-inspired comic book series, took to Instagram on Thursday (April 9) to tell fans that his "beautiful sister" Julie had passed away from cancer after a long battle with the illness.
"I'm at a loss for words. My heart hurts," the 31-year-old wrote alongside a series of sweet family photographs showing some of their travels together.
"Trying my hardest to focus on being grateful that she doesn't have to suffer any longer & remembering all the incredible times we've had together...but I just feel absolutely gutted that our family can't be together to hold one another during this crippling time. I love you."
Several of Colton's Arrowverse co-stars shared their heartfelt condolences via the comment section.
Those paying their respects included Arrow's Echo Kellum and Rick Gonzalez, Batwoman's Ruby Rose and The Flash's Robbie Amell and Grant Gustin.
Colton tragically lost his mother in March 2018, similarly taking to social media to announce the news to his fans.
"Today I lost my best friend, the love of my life...my momma," he wrote at the time.
"Words can't express how incredible this woman was. I have so many things to say but I'm in a state of shock. I will always love you momma. RIP my angel."
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