Former 'Grey's Anatomy' writer admits he doesn't know 'why we didn't kill Izzie' when Katherine Heigl left the show, according to a new book

• Katherine Heigl abruptly left "Grey's Anatomy" on season six of the show.
• In a new book, a former writer on the show admits he doesn't know "why we didn't kill Izzie."
• Heigl said that continuing to make guest appearances on the show felt like it was "manipulative."

"Grey's Anatomy" has been on ABC for 18 seasons and counting, so by now any fan of the medical drama knows that no matter how beloved a character is - no one is safe from a very dramatic death.

Katherine Heigl exited the show in 2010 after playing Dr. Izzie Stevens for six seasons. Izzie made it out of Seattle alive, but according to a new book, the character's fate could have been different.

"I don't know why we didn't kill Izzie, I really don't," Mark Wilding told Entertainment Weekly's editor at large Lynette Rice in "How to Save a Life: The Inside Story of Grey's Anatomy."

He said that there might have been "hope" in his colleagues' minds that Heigl would reprise the role one day. "Katie subsequently talked about wanting to maybe come back to the show to wrap things up a couple years later, but that never happened," Wilding continued.

But another former "Grey's" writer, Jenna Bans, said in the book that the decision not to kill Izzie was a strictly narrative choice made by creator and then-showrunner Shonda Rhimes. Bans said that she remembers the decision being made because "Shonda felt like that was more of an unexpected way to go."

Long-time fans will remember that Izzie survives cancer in season six only to then get fired from Seattle Grace-Mercy West for a mistake she believes her husband Alex Karev (Justin Chambers) is responsible for.

Izzie married Alex on season five of "Grey's Anatomy" when she thought she was dying. She only makes sporadic appearances on season six and eventually serves Alex divorce papers.

The ending doesn't provide much closure, but Heigl told Entertainment Weekly in her 2010 exit interview that the character's sudden departure "felt like the right thing to do" because she felt that continuing show up in Seattle and then leave again was "manipulative" to the audience.

On season 16, ten seasons after her original exit, we learn that Izzie (off-screen) is raising Alex's twins in Kansas. She used the embryos they had frozen while she had cancer to get pregnant.

When Chambers left the show on the season 16 episode titled "Leave a Light On," his character Alex reveals he has gone to Kansas to be with Izzie and the kids. Heigl didn't appear in that episode.

"How to Save a Life: The Inside Story of Grey's Anatomy" gives readers new insight on the most surprising character exits. It's available now.