Cloud died at age 25 on Monday.
"rest easy brother❤️🕊️," Walton wrote beneath a photo of himself and Cloud wrapped in an embrace on Instagram.
Cloud starred as Fezco on Euphoria from 2019 to 2022, on which he had pivotal storylines with Javon Walton's Ashtray and Maude Apatow's Lexi. The show also stars Zendaya, Sydney Sweeney and Jacob Elordi.
In a post to his Instagram story, Walton added that Cloud was "forever family."
Cloud's family confirmed he died on Monday in a statement to ET. He was 25. ET has reached out to Cloud's rep for further comment.
"It is with the heaviest heart that we had to say goodbye to an incredible human today. As an artist, a friend, a brother and a son, Angus was special to all of us in so many ways," the Cloud family statement read. "Last week he buried his father and intensely struggled with this loss. The only comfort we have is knowing Angus is now reunited with his dad, who was his best friend."
"Angus was open about his battle with mental health and we hope that his passing can be a reminder to others that they are not alone and should not fight this on their own in silence," the statement continued. "We hope the world remembers him for his humor, laughter and love for everyone. We ask for privacy at this time as we are still processing this devastating loss."
Meanwhile, in a statement to ET, an HBO spokesperson said, "We are incredibly saddened to learn of the passing of Angus Cloud. He was immensely talented and a beloved part of the HBO and Euphoria family. We extend our deepest condolences to his friends and family during this difficult time."