Imagining the Grey's Anatomy cast as anything other than those who we've watched across its 16-season run is a strange and somewhat impossible exercise.
But in an alternate universe, a number of the medical drama's best-loved characters could have looked very different.
Amanda Foreman - Meredith Grey
Ellen Pompeo, who has appeared in all 16 seasons (and the upcoming 17th season) of the show as Meredith Grey, didn't immediately have her heart set on joining the series.
"I was offered the role of Meredith," she told TV Guide. "I had done a movie for the studio called Moonlight Mile, so the studio was aware of me.
"Then I met Bob Orci and Alex Kurtzman. We sat down and talked about me possibly doing an arc on Alias. That didn't happen.
"Bob and Alex wrote a show called Secret Service. I really wanted to do that and the studio really wanted me to do Grey's instead.
"I read Grey's and I went and met Shonda and I decided to come on and do this. It was just an invitation and I happily accepted."
So Pompeo was always the frontrunner, but if she had turned it down, who would have stepped in?
Amanda Foreman, who is best known for playing Felicity's Meghan Rotundi, as well as appearing in Awkward and taking on minor roles in a couple of the Star Trek movies, auditioned for the role of Meredith.
She also threw her hat in the ring for Cristina Yang, but Sandra Oh was chosen for that part.
Foreman did, however, appear in Grey's 'These Arms of Mine' in season seven as Nora, the wife of Zachary, a man who had lost both of his arms during a logging accident.
Rob Lowe - Derek "McDreamy" Shepherd
Patrick Dempsey's career could have been a whole different kettle of fish had he not taken on the role of McDreamy – as could Rob Lowe's.
Chatting on WTF with Marc Maron, The West Wing star said: "Dude, I turned down Grey's Anatomy. To play McDreamy. That's probably cost me $70 million! Eh, it's just money."
But in spite of that, he has zero regrets.
"Do you know what?" he added. "Listen. At the end of the day it was like, I watched it when it came out. And when they started calling the handsome doctor 'McDreamy', I was like, 'Eh, it's not for me'."
That's the spirit.
Rhimes told the Chicago Tribune that they "brought in a lot of guys [for Shepard]", adding: "Derek was really not an easy role to cast. You had to believe he was intelligent, so you can believe he's a brain surgeon. And while you're watching, you'd be like: 'I wish my boyfriend looked like that.'
"But he had to be rugged, not pretty. Handsome, sexy, but not in an obvious way. Sexy in a smart way."
Isaiah Washington - McDreamy
Another actor who was considered for Dempsey's part was Isaiah Washington.
"You know they wanted Isaiah Washington to be my boyfriend," Pompeo told the New York Post.
"Shonda really wanted to put a Black man in the mix. I didn't think they were really going to put an interracial couple on the show and I didn't want him. It was too close to home."
For context, Pompeo is married to record producer Chris Ivery, who is Black.
Washington was eventually cast as Preston Burke, for which he won a Screen Actors Guild Award and two Image awards.
Sandra Oh - Miranda Bailey
Sandra Oh told an audience at PaleyFest in LA back in 2006 that she was originally asked to read for another character.
"I first auditioned for the part of Miranda Bailey," she said. "And thank God I did not get that part. Can you imagine not having her [Chandra Wilson, who was cast as Bailey]."
But she always had her eye on Cristina Yang.
"At that time I was practising asking for what I wanted in my life," she continued. "I saw the part of Cristina, and I wanted to do that part, and so even though producers wanted me to come in for the part of Bailey, I said, 'No, I want to come in for Cristina.'"
And the rest, as they say, is history.
Joshua Jackson - Owen Hunt
Kevin McKidd is still going strong as Owen Hunt on Grey's, but it was Joshua Jackson (Little Fires Everywhere, The Affair, Dawson's Creek) who accepted the part, with the casting announcement made back in 2007.
But then the Writers Guild of America went on strike in November that same year, which ground a number of shows, including Grey's, to a halt.
When production was back up and running in 2008, Jackson had chosen to star as the lead in Fox sci-fi series Fringe after being cast by JJ Abrams.
And who could say no to that?
Jessica Capshaw - Nurse Rose
It was Lauren Stamile who appeared as Rose, a scrub nurse who became romantically involved with McDreamy, and was essentially used by him to make Meredith jealous.
But Jessica Capshaw, who appeared on the show as Arizona Robbins until she left at the end of season 14, auditioned for that role.
And she also tried out for Sadie, Meredith's friend and an intern at Seattle Grace Hospital, who was played by Melissa George.
But the third time, as we all know, is the charm and Capshaw was later cast as Arizona.
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