"Grey's Anatomy" star Isaiah Washington is revisiting his years-long feud with former co-star Katherine Heigl.

The two appeared on the medical drama together during its early seasons. Taking to Twitter on Monday, Washington recalled the time Heigl reportedly said Washington should not speak in public.

"This woman once proclaimed that I should ‘never’ be allowed to speak publicly again. The world agreed with her proclamation back then and protested for my job and my head in 65 languages. I wish I was on Twitter in 2007, because I will NEVER stop exercising my free speech," Washington tweeted with a photo of Heigl.

It's unclear what prompted Washington to speak out about Heigl.

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In another tweet, Washington clapped back at a follower who defended Heigl. He said Heigl was not defending her gay friend, and dragged actress Chandra Wilson into the drama, writing she "knows all about that too."

When one follower asked Washington why he was bringing the drama back up 10 years later, he wrote, "Because it's the TRUTH. The End."

Meanwhile, a source close to Heigl told Fox News: "Katherine stood up for her close friend twice when Isaiah publicly outed him and called him a f-----. That’s hate talk, not free speech. She is proud that she stood up for him. Katherine is and always will be an advocate and ally to LGBTQ community."

The former co-stars' feud dates back to 2007, when Heigl claimed Washington made an anti-gay slur on set against "Grey's Anatomy" star T.R. Knight.

Katherine Heigl's past drama with 'Grey's Anatomy' co-star Isaiah Washington was reignited on Monday.

Katherine Heigl's past drama with 'Grey's Anatomy' co-star Isaiah Washington was reignited on Monday. (Getty)

Heigl, known for her role as Dr. Izzie Stevens on the ABC drama, said the slur left her "furious and frustrated." She also claimed in an interview with Entertainment Weekly that Washington apologized to her on set over the feud.

"Isaiah thanked me, which I didn't understand," she told the outlet. "He was almost grateful. I don't know Isaiah well, but he takes his work seriously and he loves his character."

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Isaiah Washington previously denied Heigl's claim that he used an anti-gay slur on set of the ABC medical drama.

Isaiah Washington previously denied Heigl's claim that he used an anti-gay slur on set of the ABC medical drama. (Alberto E. Rodriguez/Getty Images)

Washington reportedly denied making the slur at the Golden Globe Awards that same year.

Washington exited the show after Season 3 following the accusation. While speaking about his departure on the Fox Nation series "Isaiah Washington: Kitchen Talk" in July, he explained why he decided to publicly apologize for the incident.

"The story was a lie and misconstrued. But as a family guy, a father, I thought I was helping the family," said Washington.

He also said he wouldn't ever apologize for it again.

"That's why I'll never apologize again -- to this day," said Washington. "That's why Trump doesn't apologize, because when you apologize for something, then that it is admitted to wrong -- doing something wrong. I did nothing wrong."

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Meanwhile, Heigl's last appearance on the show was in January 2010, two years after she reportedly ruffled feathers for pulling her name from an Emmy contention. She later told radio icon Howard Stern that she didn't pull her name, and instead never submitted herself in the first place because she wasn't proud of her performance. She claimed it had to do with a lack of "emotional material" for her character.

In a recent interview with the Los Angeles Times, showrunner Krita Vernoff recalled having to rewrite the script after Heigl did not appear for her farewell episode.

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“All I know is that the night before a thing is supposed to start shooting that is entirely centered on one character and the completion of her story arc, I got a phone call that she wasn’t coming to do it. That’s what it is to be a TV writer and producer. So, yeah, do I wish I could go back and do that differently? Sure," Vernoff told the outlet. 

A source close to Heigl, however, denied Vernoff's claim, calling it untrue.

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"Grey's Anatomy" is currently in its 17th season, and its recent premiere episode shocked fans with the return of Dr. Derek Shepherd, played by Patrick Dempsey.

Reps for Heigl, Washington and Wilson did not immediately respond to Fox News' request for comment.