13 years after Katherine Heigl left Grey's Anatomy, she and Ellen Pompeo have reunited to talk about it.

It's the Grey's Anatomy reunion we've been waiting for.

Katherine Heigl and Ellen Pompeo have come together as part of Variety's 'Actors on Actors' interview series, where two stars — sometimes with absolutely no connection, and sometimes with decades of history — simply chat.

Obviously, the former Grey's Anatomy co-stars very much fit in that second camp. There's a lot to unpack here.

Recently, Pompeo left Grey's Anatomy (she still narrates) for the first time since the series began in 2005. 

Heigl departed in 2010, after several years criticising the work environment. In 2009, she said that the Grey's cast had been asked to work 17-hour days, describing the work conditions as "mean and cruel", and made several other headlines that saw her labelled a "diva" and "difficult".

Watch: Katherine Heigl on being labelled 'rude'. Post continues below video.

It's far from the only Grey's Anatomy drama, but it's certainly one of the most enduring. 

Last year, Pompeo stated that her co-star had been "ahead of her time", and their bond clearly remains in their hour-long discussion for Variety.

Here is what we learned.

Katherine Heigl didn't expect to become the 'villain'.

In 2010, Heigl left the show following public complaints about the long hours on set and after withdrawing her name from Emmy contention, stating that she did not think her character Izzie's storylines were Emmy-worthy.

Heigl told Pompeo that the success of Grey's Anatomy gave her "confidence that was a false sense of confidence".

"It was rooted in something that couldn't and maybe wouldn't always last for me. So then I started getting real mouthy, because I did have a lot to say, and there were certain boundaries and things that I was not okay with being crossed. I didn't know how to fight that."

It earned her a reputation for being 'difficult', especially as every detail of this time was reported in the press, that has followed her ever since.

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Now 44, Heigl told Pompeo she has become "comfortable with my role as the villain" in recent years.

"I was in my late 20s. It took me until probably my mid- to late-30s to really get back to tuning out all of the noise and going, 'But who are you? Are you this bad person? Are you ungrateful? Are you unprofessional? Are you difficult?' Because I was confused! I thought maybe I was," she explained.

She said she was "so naïve" to think she could speak her mind and have it be well-received.

"I got on my soapbox and I had some things to say, and I felt really passionate about this stuff. I felt really strongly. I felt so strongly that I also got a megaphone out on my soapbox. There was no part of me that imagined a bad reaction. I felt really justified in how I felt about it and where I was coming from. 

"I've spent most of my life — I think most women do — being in that people-pleasing mode. It's really disconcerting when you feel like you have really displeased everybody. It was not my intention to do so, but I had some things to say, and I didn't think I was going to get such a strong reaction."

Pompeo's biggest issue with Meredith Grey.

In season 19 of Grey's, Meredith and her children moved to Boston, although Pompeo has said she hopes to return for appearances next year.

She said she was "happy" to let Meredith go, citing her character's inability to make relationships work one of her "frustrations".

"Somehow, Meredith can’t figure out how to make a relationship work, still, after all this time. And I guess if she were to make it work, then where's the conflict? There has to be conflict. It's not that I don't think there shouldn't be conflict. There should be conflict. I guess I just have different ideas of about what the conflict should be."

She said she felt "so happy to be able to step away" and felt like she'd accomplished something incredible.

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The ghost sex scene (and the deer scene).

Grey's Anatomy fans will have certain storylines burnt into their brains — and two of the most outlandish involved Dr Izzie Stevens.

Of course, there was the infamous ghost sex scene in season five. If you know, you know.

Pompeo told Heigl she had been watching Grey's with her, leading Heigl to say she'd be too embarrassed to watch certain scenes with her kids.

"Yeah. This is sex with the ghost," Pompeo said.

"Yeah, that. The oral sex with the ghost while somebody else was watching in the room. I don’t know how I’d explain that."

They then talked about another of Izzie's memorable episodes... the one where she saved the life of a deer. It's difficult to find vets in Seattle, apparently.

Turns out, Heigl worked with that particular deer twice.

"I worked with that deer years later in a different show I was doing. I'm like, 'I know that deer. I saved that deer on Grey's Anatomy.'"

Being the original 'pick me' girl.

Meredith Grey's "pick me, choose me" scene is perhaps the most memorable Meredith moment of all time (and she's been there for 200 years, so there's a lot to choose from!).

In season two, episode five, Meredith begs Patrick Dempsey's character Derek Shepherd to sign his divorce papers and be with her.

The scene is iconic, but Pompeo hated it.

"My daughter and her friends, they sit around and they’re like, 'Oh, she's a 'pick me girl,'," she said, joking that she invented 'pick me' girls.

"I fought that speech so hard. That's another really interesting thing about life is some things that I was so against, and I was like, 'Why would I beg a man - I can't beg a man on TV! This is so embarrassing,' And then it turns out to be one of the most successful scenes or famous scenes ever."

She continued: "In the scene, I’m crying, but I'm really crying because I have to beg a man on television."

Feature image: ABC/Variety.