"I have nightmares." Pauley Perrette accuses NCIS co-star Mark Harmon of attacking her.

Pauley Perrette, 50, has shared she will never return to NCIS because she is terrified of her former co-star Mark Harmon, 67.

Perrette, who played the forensic scientist Abby Sciuto for 15 seasons, announced she was leaving NCIS in October 2017.

Her departure announcement gave little reasoning, but the actress did insist the “network and show are not mad at me”.

Now, almost two years after exiting the show, the actress isn’t holding back. She has revealed on Twitter that Mark Harmon, who plays the show’s lead Leroy Jethro Gibbs, was a significant reason for her departure.

“NO I AM NOT COMING BACK! EVER!” she wrote to her Twitter followers. “(Please stop asking?) I am terrified of Harmon and him attacking me. I have nightmares about it. I have a new show that is SAFE AND HAPPY! You’ll love it! #HappyPlace Love y’all!”

NO I AM NOT COMING BACK! EVER! (Please stop asking?) I am terrified of Harmon and him attacking me. I have nightmares about it. I have a new show that is SAFE AND HAPPY! You’ll love it!#HappyPlace Love y’all!

— Pauley Perrette (@PauleyP) June 7, 2019

In a since deleted tweet, Perrette went on to expand on an alleged assault against one of the crew members, and provided pictures of the aftermath.

“You think I didn’t expect blow back? You got me wrong,” she wrote. “THIS happened To my crew member and I fought like hell to keep it from happening again! To protect my crew! And then I was physically assaulted for saying NO!? and I lost my job.”

Reports say it was Harmon’s dog that was responsible for this attack.

According to a previous source speaking to Radar in October 2016, Harmon brought a rescue dog pitbull to the set and it bit a crew member, causing a gash that required stitches to mend.

When Harmon later brought the dog back to the set because he had no one to look after it, the source said Perrette was “furious” and from then on refused to work with the actor.

It was one year after this that she announced her departure.

This is not the first time Perrette has alluded to a toxic environment on the NCIS set as contributing to her exit from the show.

“I refused to go low, that’s why I’ve never told publicly what happened," she told her Twitter followers in May 2018. "But there are tabloid articles out there that are telling total lies about me. If you believe them? Please leave me alone. You clearly don’t know me. (Sorry guys, had to be said)"

She continued: "Maybe I’m wrong for not 'spilling the beans' Telling the story, THE TRUTH. I feel I have to protect my crew, jobs and so many people. But at what cost? I.don’t know. Just know, I’m trying to do the right thing, but maybe silence isn’t the right thing about crime. I’m… Just… ?"

I refused to go low, that's why I've never told publicly what happened. But there are tabloid articles out there that are telling total lies about me. If you believe them? Please leave me alone. You clearly don't know me. (Sorry guys, had to be said)

— Pauley Perrette (@PauleyP) May 13, 2018

These tweets started whispers that Perrette had been the victim of workplace bullying during her time on NCIS. Although once mere rumours, Perrette has now confirmed that it was Mark Harmon who she was so terrified of.

Harmon has not responded publicly to Perrette.