Christian Bale's former personal assistant spoke out exclusively to INSIDE EDITION about the star's explosive temper.

Bale's shocking tirade on the set of his new movie Terminator Salvation comes as no surprise to Harrison Cheung. He worked for the actor for nine years and says they were once close friends.

According to Cheung, "I think [Bale] can be extremely hot-headed. You know, he's over 6'1" and he could be very intimidating."

Cheung is a self-described computer geek who first entered Bale's life in 1994, when he sent a fan letter and then set up his official website. 

Before long, he was doing everything for the actor, until they had a falling out and parted ways in 2003. 

"Christian is a very prickly professionalist," he says.

The former assistant says Bale developed a reputation for bad behavior on movie sets. What really set him off, Cheung says, were disruptions when he was preparing to shoot a scene. This explanation seems right on par with what appears to have happened before his shocking just released profanity-laced tirade.

Cheung says, "He was always very deep in thought and he didn't want to be disturbed…if he heard any unusual noises or if someone asked him to move around too many times, you could tell he was getting irritated. The big 'Do Not Disturb' sign was on his forehead."

Now an IBM computer consultant, Cheung says he's coming forward to set the record straight about the star he used to work for. So does Cheung fear that talking to INSIDE EDITION will be seen as a betrayal to the actor? "I've been loyal to Christian for a long time, and when he and I worked together I kept that trust. I no longer work with him so it's a different situation now."