In a new excerpt from the book "How to Save a Life: The Inside Story of Grey's Anatomy", the actor confirmed the rumours that Pompeo didn't want a black love interest on the show.
Patrick Dempsey landed the role of Meredith Grey's future husband, neurosurgeon Dr. Derek Shepherd, and Isaiah accepted it would have been uncomfortable for Ellen to have an interracial romance on the show while dating an African-American in real life.
"(Series creator) Shonda (Rhimes) and I thought it was a great idea to represent a brain surgeon who looked like (retired black American neurosurgeon and politician) Dr. Ben Carson," Washington says. "That didn't go that way."
But Isaiah, who ended up being cast as cardiothoracic surgeon Dr. Preston Burke, supported Pompeo's decision.
"There's a rumour out there or something that Ellen didn't want me to be her love interest, because she had a black boyfriend," he says in the book. "I guess she implied that her boyfriend may have had a problem with her doing love scenes with me, so she felt uncomfortable... I supported her with that."
At the time, Pompeo was dating her now-husband Chris Ivery. She and the music producer tied the knot in 2007 and have three children together.
Ellen told the New York Post in 2013 why she passed on having Isaiah as her onscreen boyfriend.
"You know they wanted Isaiah Washington to be my boyfriend. Shonda really wanted to put a black man in the mix," she said. "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."