FAST & FURIOUS star PAUL WALKER had a shocking secret he took to his grave – his “friendship” with co-star Vin Diesel was a total farce!

In real life, there was no love lost between the two, sources told The ENQUIRER.

Since 2001, Walker, 40, and Diesel, 46, starred alongside each other in the hugely popular movie series about illegal street racing. The seventh installment was being shot when Walker was killed Nov. 30 in a fiery car crash.

After the accident, Diesel posted an online message saying: “Brother I will miss you very much. I am absolutely speechless.”

But sources say behind the scenes their egos frequently clashed to the point that “Paul often couldn’t stand to be in the same room with Vin,” revealed a close source. “He didn’t openly badmouth him, but what millions of fans never knew is Paul really couldn’t stand Vin.

Paul was convinced Vin was trying to outdo him – stealing the limelight and fawning all over the producers so they’d make him look good.

“He considered Vin to be very self-centered.”

Even on screen, the two actors were complete opposites, with Walker playing an undercover cop and Diesel in the role of an ex-convict who’s also an elite street racer.

Tensions between the two apparently hit a fever pitch on the set of “Fast & Furious 6.”

“They ignored each other and refused to speak – sometimes for days,” revealed the close source.

Just days before his untimely death, Walker summed up their relationship. In an interview, he said the two men had respect for each other but added: “There are certain days I still want to crack him in the head…and there are days he wants to crack me in the head, too!”