Ketterer is a pediatric nurse living with his wife and six kids in Orange County, California, and he wowed the judges earlier in the competition with both his incredible voice and his emotional backstory.
Ketterer and his wife are the parents of six children, including their biological daughter, Sophie, and five sons that the pair adopted from foster care and took into their home to give them the stable family life they'd not had until living with the Ketterers.
During the second week of the AGT quarterfinals on Tuesday, Ketterer was the last act of the night and belted out an emotional rendition of James Bay's "Us" that captivated the audience and earned a standing ovation when he sang the final notes.
Though he tried to get Banks to go to someone else first, the host persisted so that Cowell would share his real, unbridled feelings about Ketterer and his performance.
"As I dad, I can't imagine [doing] what you've done, and the fact that you're on this show and you really need this. You're a really, really special guy," Cowell said, as his voice cracked with emotion and his eyes welled up with tears. "There's just something about you."
"That was one of the most beautiful moments I've ever seen from you, that vulnerability and that beauty," Banks said. "That's what a lot of people don't know about Mr. Cowell, is that he is a big soft papa."
Mel B got choked up a bit as well, and had to take a second to compose herself before sharing her thoughts.
"You're just an incredible person and an incredible human being," the former Spice Girls star said while she tried to hold back tears. "To do what you've done, adopting all these kids and giving them a life, and then your voice sings such truth and honestly."
Fellow judges Heidi Klum and Howie Mandel were blown away by Ketterer's inspirational actions and celebrated the contestant for the message he sends to other people watching the show.
"When you sing, you sing with so much heart," Klum said. "And on a side note, we just need more men like you."
"This is not a sob story, this is a happy story," Mandel added. "People should be led and inspired by who you are and how you are."
Banks then asked the singer how he felt about bringing Cowell to tears, and Ketterer said "I think he gets it."
"These are my babies, and I have given my entire life to this," Ketterer said, fighting back tears himself, before giving a shout out to his lady love in the audience. "I couldn't have done it without my wife, she's one of my greatest supports."
Following the show, ET's Denny Directo caught up with Cowell, who said he was "trying to keep it together" while giving his feedback.
"That normally doesn’t happen to me, but there’s something about Michael," Cowell shared. "[Especially] now that I’ve gotten to know him and what it means to him."
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'America's Got Talent': Father of 6 Earns a Golden Buzzer From Simon Cowell
"It’s his sincerity, his kindness and what he’s done to change those kids' lives, and then he puts it all out on the line tonight and I really felt for him, he’s a really special person," Cowell added.
ET also spoke with Mandel, who revealed that Cowell's emotional reaction didn't surprise him at all, and hinted that the British TV personality's reputation for having an acerbic personality may be unfounded.
"I’ve gotten to know Simon personally over the last couple of years and I don’t think people know what kind of a human being and what kind of a father he is and what kind of a friend he is," Mandel shared. "So many times when he’s just been doing his job and he feels that maybe somebody was hurt by something he said, we go to commercial and he’ll jump up on the stage and give them a hug and make sure they feel good and [give them some] encouragement. He is the first one up there."
"He is the biggest softie, so when you see somebody that is this aspirational, inspirational in what they’re doing -- and [Simon] does a lot of good charitable things for children that aren’t spoken about -- he doesn’t do it for the cameras -- I just thought, 'Oh, my God, this is Simon's lane,' This is exactly what he aspires to be."
"It's really been surreal," he admitted. "I did not expect the amount of just people wanting to get in touch with me... I had no idea this would happen." For more from Ketterer's emotional interview, check out the video below.