Harry Potter billionaire J.K. Rowling’s staff were “terrified” of the author’s wild mood swings, a former personal assistant has testified.

As well she might.

Amanda Donaldson, 35, is accused of stealing more than $40,000 from Rowling. Donaldson has denied using the author’s credit card on a wild spending spree.

The former PA told a British court that Rowling was “unapproachable” and staff were wary of her unpredictable moods.

“Approachable isn’t something I would say,” Donaldson said of the writer. “People in the office would sometimes ask if she was in a good mood, in a terrified way.”

She insisted the purchases she made were for the business and done while Rowling was penning her next bestseller.

Rowling’s husband, Dr. Neil Murray, earlier slammed Donaldson as a “liar” and accused her of stealing Harry Potter merchandise stored in the office that was to be sent to sick children.

But Donaldson said Rowling had asked her to buy cards, gift wrapping and cakes and coffees for business meetings and staff birthdays.

Donaldson added that Rowling “could be really generous” and even bought her a replacement stroller when her child’s original was damaged.

Rowling is seeking damages in the civil case she brought under her married name, Joanne Murray.

As for the company credit card, the former PA said she never received specific instructions about its use and wasn’t allowed to bother Rowling, so she made her own decisions.

“It was my understanding I would make the decision and would tell her after what I had done. I was never told otherwise,” Donaldson said.

“I really respected my role and would never have dreamed of doing anything like that (stealing Harry Potter swag). I’m quite offended and hurt.”