(Cover) - EN Showbiz - Johnny Knoxville has revealed his grief following the death of his Jackass co-star Ryan Dunn, saying he has "lost a brother".

Dunn and an as-yet unidentified passenger died after the star's Porsche crashed into a tree and burst into flames in Pennsylvania, in the early hours of this morning. He had recently celebrated his 34th birthday and his close pal Knoxville has paid tribute to the star via his Twitter account.

"Today I lost my brother, Ryan Dunn. My heart goes out to his family and his beloved Angie," Knoxville, 40, wrote. "RIP Ryan. I love you buddy."

Fellow Jackass star Wee-Man real name Jason Acuna - has also revealed his heartbreak in the wake of Dunn's death.

"I miss you, bud," Acuna, 38, wrote on Twitter. "You were always a happy kick-ass dude!"

Dunn's close pal and Jackass co-star Steve-O is believed to be inconsolable following the accident and he has so far been unable to comment on his passing.

Good Charlotte guitarist Benji Madden has joined a host of other stars in paying tribute to Dunn. "I'm very Sad and Shocked to hear about Ryan Dunn," Madden Tweeted. "My thoughts&Prayers are with his Family."

Reality TV star Brody Jenner wrote, "Just heard about Ryan Dunn So sad.. #RIPRYANDUNN."

Upon arrival at the scene earlier today, police reportedly found a 2007 Porsche 911 GT3 "off the road and in the woods that was fully engulfed in flames".

Dunn's male passenger was also pronounced dead at the scene, but his identity will not be revealed until his family have been informed. Both men are believed to have died at around 3am "as a result of injuries sustained in the accident".

An official police report has revealed that "preliminary investigation revealed that speed may have been a contributing factor to the accident".

MTV who broadcast the popular Jackass television series have also paid tribute to Dunn, saying he will be sorely missed.

"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, said in a statement.

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