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"Grey's Anatomy's" Jessica Capshaw

Grey's Anatomy showrunner Shonda Rhimes defended her creative decision to amputate the leg of a fan favorite character, and vowing that the story line would indeed have a happy ending.

During the ABC medical drama's eighth-season finale, Meredith (Ellen Pompeo), Derek (Patrick Dempsey), Cristina (Sandra Oh), Arizona (Jessica Capshaw) and Mark (Eric Dane) were left stranded after their plane crashed heading from Seattle to Boise, with Lexie (Chyler Leigh) failing to make it out alive.

Season nine picked up to flash-forward after the crash, revealing not only that Mark would succumb to the internal injuries sustained in the crash but also that Arizona -- who was left with a severe injury to her leg (bone was exposed) -- would eventually lose the limb after an infection threatened her life.

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"It felt real to me that Arizona would lose her leg," Rhimes wrote late Thursday on her Shondaland blog. "That someone we love so much would go from being ambulatory to WORKING on being ambulatory, that we would begin to understand what it is like to be differently-abled from watching a person we love BECOME differently-abled."

During Thursday's episode, which flashed back to reveal how the survivors were rescued and fill in the blanks between the crash and the events in the premiere, Arizona asked that her wife Callie (Sara Ramirez) promise that she wouldn't allow her leg to be amputated. However, as Callie is performing surgery on Derek's injured hand, Arizona crashes and Alex -- whom Arizona replaced on the doomed flight -- is forced to cut off Arizona's leg in order to save her life, thus putting Callie on the hot seat with her partner.

"It must be terribly difficult to be Callie right now. To have your partner hate you. To have your sex life taken away. To have your BEST FRIEND taken away," Rhimes wrote. "Arizona has been taken from her and Callie is doing her best to survive that."

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'Grey's Anatomy's' Shonda Rhimes: Arizona Will 'Get Her Mojo Back'