REFORMED badboy Jason Priestley describes his former Beverly Hills, 90210 co-star Shannen  Doherty as a witch on wheels in a gripping new tell-all.

Priestley, 44, who shot to fame playing clean-cut Brandon Walsh on the popular nighttime soap that aired from 1990 to 2000, trashes co-star Doherty, his TV “sister.”

He’ll never forget the time FOX executives sent the pair by private jet on a last-minute trip from L.A.

to New York City to meet with advertisers. In “Jason Priestley: A  Memoir”, the Canadian-born actor

recalls, “I could not believe my ears at Shannen’s very first words after she boarded. Her butt had barely hit her seat before she said loudly to the PR person, ‘Really? A (Lincoln) Town Car? You send a Town Car to take me to the airport, not a limo?’

“But that was just the beginning,” he adds.

“I looked on, becoming more uneasy by the minute as she began bitching about the short notice and the food on board and the temperature in the cabin and everything else.”

Mischa Barton was another spoiled-rotten brat, he claims in the book. In 2004, Priestley, then starring on FOX’s “Tru Calling”, hopped a ride with “The O.C.” actress and her mother during a press event for their network in the Bahamas. He claims Barton threw a hissy-fit and loudly asked her mom, “‘Do we have to share a car with HIM?’ We had a very silent 30-minute ride,” he writes.

But one of his “high” points came when he smoked pot with Mick Jagger and the rocker’s then-wife Jerry Hall, following a 2000 awards show in Dublin, Ireland.

They were at a star-studded bash at The Clarence Hotel and he remembers the couple  “lounging on a bed, passing a joint back and forth.” Jagger eventually got up and handed it to Priestley and he “took a drag.”

The hunky dad of two, who’s married to second wife Naomi Lowde, also dishes the dirt, quite literally, on Brad Pitt.

In 1987, when both were virtually unknown, Pitt temporarily moved in with Priestley and his roommate, crashing on their couch. “Just for fun, we used to have competitions over who could go the longest without showering and shaving,” he writes.

“Brad always won. Having to go on an audition meant cleaning up, which is what usually put an end to the streak.”