Rob Dyrdek is speaking out after the shocking death of his beloved friend and former Rob & Big co-star Christopher "Big Black" Boykin, who passed away on Tuesday morning at the age of 45. 

"My heart is broken. I don't want to write this post. I don't want to believe that this is reality," he wrote on social media. "I am so thankful for you."

The MTV star added, "We truly were brothers that lived an unexpected unforgettable adventure. I just can't fathom that it would end so suddenly. You will forever be in my heart."

Big Black rose to fame as the professional skateboarder-turned-TV host's bodyguard on the wildly popular MTV series, which ran for three seasons from 2006-2008.

The unlikely duo's onscreen antics led to two spin-off series, Rob Dyrdek's Fantasy Factory and Ridiculousness, which Big Black made several appearances on. He also popped up on MTV shows Guy Code and Snack Off.

"I am so thankful for this moment..." Rob also shared on Twitter Tuesday night with a photo of Big Black holding his baby. "Thank you for being an amazing human being and brother."