Izzie's iconic pink prom dress on 'Grey's Anatomy' had to be custom-made by a wedding-dress designer because Shonda Rhimes kept wanting it to be 'bigger'

• Shonda Rhimes wanted Izzie's prom dress to be "bigger" on the "Grey's Anatomy" season-two finale.
• According to a new book, the rose-pink dress ended up being custom-made by Amsale.

One of the most heartbreaking scenes in "Grey's Anatomy" history is also the most visually stunning thanks to an iconic pink "prom" dress that almost never saw the light of day.

On the show's season-two finale, "Losing My Religion," Izzie (Katherine Heigl) and the other interns are attending the prom they planned for the niece of Dr. Richard Webber (James Pickens Jr.) at the hospital when Izzie's fiancé, Denny Duquette (Jeffrey Dean Morgan), dies of an apparent stroke caused by complications after heart-transplant surgery.

Upon finding him dead in his hospital bed, Izzie climbs in to be with him, huge, rose-pink dress and all. Alex Karev (Justin Chambers) has to gently lift her to extract her from her place beside Denny's body, gathering all of the layers in his arms.

According to "How to Save a Life: The Inside Story of Grey's Anatomy" by the Entertainment Weekly editor at large Lynette Rice, the show's costume designer Mimi Melgaard struggled to find the perfect dress for Izzie to wear during the tragic moment because the series creator and then-showrunner, Shonda Rhimes, had a specific vision in mind.

"That year in Los Angeles, all the dresses were very gauzy and long and soft," Melgaard said, according to the book. "I'd fit Katie in dresses and Shonda would be like: 'No, no. I want bigger.'"

Melgaard was pressed for time and couldn't find anything to Rhimes' liking on her own. She ended up having to call the famed wedding-dress brand Amsale and asked it to make the dress in a week.

But the time crunch and the stress of securing the pink gown with the stunning broach accent were worth it for the art it helped create, according to the costume designer. "When you see the shot of Izzie in the elevator, and then Izzie lying across Denny, and then the shot of Alex holding her with her dress hanging down ... those are the shots that Shonda saw in her head," Melgaard said.

Melgaard said Rhimes wanted a "beautiful princess dress" that "had its own voice" to create a "Cinderella" moment for Izzie.

They couldn't have known it at the time, but Melgaard, Rhimes, and Amsale together created a dress that's had a life beyond "Grey's Anatomy." "It went to Disney World in Florida for a long time," Melgaard said, according to the book. "It goes on tour. That dress tours places!"