Weeks ago, after Ketterer's powerful performance during the quarter-finals round, Simon Cowell called out Brooks and challenged him to pen an original tune for the hopeful to sing during the finals.
Brooks responded to the challenge a few weeks later during a Facebook Live video, where he revealed that he'd spoken with Ketterer and was working on writing something specifically for him, but admitted that it might not come together before the finals.
When Ketterer came out during the final night of performances on Tuesday, he delivered a raw, emotional rendition of the soul classic, "Ain't No Mountain High Enough." And while it was warmly received, some were disappointed that the collaboration with Brooks didn't come together.
Which is why Ketterer's mind-blowing follow-up on Wednesday, where he penned an amazing new song called "The Courage to Love," wowed the judges and earned a standing ovation from the audience.
"I cannot tell you how much I love you for what you did for this man," Cowell said after Ketterer's incredible appearance.
Before he took the stage, a pre-taped package included the moment Ketterer got a call from Brooks over FaceTime, and the hopeful was blown away that his AGT journey led to him getting the kind of opportunity he never imagined.
"Sure ain't a bad way to leave the Dolby [Theater], singing a song written by Garth Brooks," Ketterer said with a stunned and thankful laugh.
This won't be the last time the inspiring singer -- who is a pediatric nurse and father of six -- will be working with Brooks. The country superstar recently invited Ketterer to perform with him at his sold-out Notre Dame Stadium concert on Oct. 20.
For more on how Ketterer's collaboration with Brooks came to be, check out the video below.