Robert Downey Jr. is grieving over the death of his assistant Jimmy Rich, who passed away in a fatal car accident on Wednesday night. He was only 52 years old.

“This is not news. This is a terrible and shocking tragedy,” Downey wrote on Instagram. “He was a brother, my right hand man, an uncle to our kids and beloved by all who experienced his singular character and wit.” Downey also thanked Rich for supporting “every step of my recovery, life and career.”

According to Deadline, the pair started working together in 2003, when Downey was in the 2003 film The Singing Detective. Rich would soon become Downey’s right-hand for a total of 22 feature-length projects, including every Tony Stark flick for Marvel.

Other Avenger stars and actors paid their respects, with Chris Evans paying tribute to Rich, as well as Marvel Studios’ official Instagram page.

Mark Ruffalo, Chris Pratt, Josh Brolin, Jeremy Renner, Jack Black, Ryan Reynolds, and Clark Gregg shared their condolences underneath Downey’s IG post. Ruffalo thanked Rich “for always being real, always being there to lend a hand and showing the way of light forward to so many people.” Elsewhere, Black said Rich was a “good man,” Pratt said Rich was “awesome,” and Reynolds said his death was “heartbreaking.”