Credit: Ron Galella, Ltd./

It's a somber day for the Jackass boys.

After Johnny Knoxville learned that his friend and MTV costar Ryan Dunn died in a Pennsylvania car crash early Monday morning, the 40-year-old daredevil took to Twitter to express his grief.

"Today I lost my brother, Ryan Dunn. My heart goes out to his family and his beloved Angie," Knoxville wrote. "RIP Ryan. I love you buddy."

Wee-Man (real name: Jason Acuna) also shared his condolences via the social networking site. "I miss you, bud," Acuna, 38, wrote. "You were always a happy kick-ass dude!"

Added Dave England, 41: "I love you Ryan. I'm gonna miss you bad."

Police told TMZ that 34-year-old Dunn's 2007 Porsche 911 GT3 was found "off the road and in the woods" in West Goshen Township. Dunn and an unidentified passenger lost their lives around 3 a.m. "as a result of injuries sustained in the accident."

It's unclear whether alcohol was involved, though Dunn tweeted a picture of himself drinking with pals late Sunday. Officers believe "speed may have been a contributing factor" in the accident.

"We are devastated by the tragic loss of Ryan Dunn, a beloved member of the MTV family for more than a decade," Van Toffler, President of MTV Networks Music/Films Group tells Us Weekly in a statement.

"He made us all laugh and had the tireless enthusiastic approach to life of your favorite middle school friend. Our thoughts and deepest condolences are with Ryan's family and friends. The Jackass brotherhood will never be the same."