As it turns out, Lea Michele chose the song "Make You Feel My Love" for the special, with Glee creator Ryan Murphy telling Australia's TV Week, "It was a very personal one for her and Cory."
"She's ultimately the person who approved and chose that song," Ryan continued. "She wanted to do something personal. I don't think she'll ever share why she chose that song. It was very sad; everybody was wrecked. It was really hard."
In the episode, the cast returns for Finn Hudson (Cory)'s memorial, in the wake of his passing.
And although Lea only appears towards the latter part of the episode, she was there for the entire filming, Ryan said.
"She was actually deeply in it [on set]--her story kicks in during the last half. It was very brave of her to do, because there were some cast members, who we won't name, who didn't want to do a grief episode, didn't want to do a memorial episode. So, Lea really put herself in the bottom of the heap and soldiered on."
Ryan said producing the episode was a heavy task, with many of the cast members so "shattered" during filming that they could only shoot one take of certain scenes.
The TV exec went on to say he wanted to make sure he handled the content in the right way considering that he not only wanted to honor Cory but also to show teens how to handle a loss like that.
"The episode is about how you mourn people and how lives can make a difference," Ryan continued, adding, "Particularly with the Rachel character, she struggles with it [the loss] all season. It's not just done, buried and goodbye."
Watch the preview for "The Quarterback" here.