Pauley Perrette left NCIS in 2018 after 15 seasons as Abby Sciuto opposite Mark Harmon's Gibbs. There were definitely rumors of tension toward the end, but it was still a shock when Perrette mentioned Harmon by name in a June 2019 tweet telling fans why she'll never return to NCIS. CBS president of entertainment Kelly Kahl was recently asked about Perrette's tweet and basically echoed what the network had said before, while noting that Perrette can't be that unhappy with CBS if she's coming back for a new show called Broke.
Here's what Pauley Perrette had tweeted on June 7:
Here's what CBS boss Kelly Kahl told reporters after the network's 2019 TCA panel (via Deadline):
I can’t speak to what she’s addressing in her tweets. She came to us with a workplace concern, we immediately investigated it and resolved it to everyone’s satisfaction, and we’re very happy to have her on the air with us this year. I don’t think she’d be back with us if she had huge concerns.
Pauley Perrette had tweeted in May 2018 about multiple physical assaults, without naming names, suggesting that was why she was leaving NCIS. According to TheWrap, the drama between Mark Harmon and Pauley Perrette can be sourced to an incident in 2016 where Harmon’s dog bit a member of the crew, requiring 15 stitches. Perrette reportedly wasn't happy when the dog was allowed to return to the set afterward.
After her 2018 tweets, CBS responded by saying Pauley Perrette had come to them with a workplace concern, and they took the matter seriously and worked to find a resolution. Pauley replied to that by tweeting:
I want to thank my studio and network CBS They have always been so good to me and always had my back.
So it does sound like she's not mad at CBS, but she did call out Mark Harmon by name in her 2019 tweet. After she openly dragged him into the conversation, rumors came out that Harmon wanted CBS to back him up. He is still the main star of NCIS and her suggestions could certainly be seen as painting him in a bad light. So far, though, he has not addressed Pauley Perrette's comments.
Meanwhile, Pauley Perrette is busy promoting her new comedy Broke:
Broke has yet to announce a premiere date on CBS, but it's expected midseason. NCIS Season 17 is now filming, still starring Mark Harmon, and will premiere Tuesday, September 24, 2019 at 8 p.m. ET on CBS.