"I really thought Jackie had it in the bag," a still-in-shock Grimm told PEOPLE after winning the $1 million prize and top billing at the upcoming AGT tour, which will stop for a show in Las Vegas. "I was preparing my speech to leave. I couldn't believe I heard my name. I was trying to make sure that what I thought was going on was going on, you know? This is definitely an out-of-body experience. This whole journey has been, but especially now."
Judge Piers Morgan insisted Grimm's victory was well deserved: "Michael's genuine, he's sincere, he's very talented, he got better with every round, and [on Tuesday] night he gave the performance of his life. He'll have a huge career. I think he's like a young Van Morrison."
And Evancho is the new Susan Boyle, Morgan believes. "Everyone assumed Susan was going to win [Britain's Got Talent] and she finished second," he said. "Now she's sold millions of albums. Jackie's going to have a superstar's career."
Struggling musician Grimm, 30, captured viewers' hearts with his soulful pipes and humble struggles: Raised by his grandparents, who lost nearly everything in Hurricane Katrina, he entered Talent with the hopes of being able to buy them a new home. It's a promise he intends to keep. "My grandparents don't have to worry about anything anymore," he said, tears filling his eyes. "I can't put into words what that means to me. They've supported me in the music through the years, and they've seen me fall and get back up and keep going. Now I can take care of them."
And they're not the only ones. Grimm revealed he plans to propose to Lucy, his girlfriend of nearly three years and the inspiration for his performance of "When a Man Loves a Woman" during Tuesday's finals. "That's my girl," he said, "and I'm not gonna let that one go."
But even a nearly-engaged guy has crushes, and Grimm got to perform with one of his – Jewel – during the finale. "She's amazing," he said of his duet partner on "Me and Bobby McGee." "She made me feel so comfortable on stage. But [at one point] she smiled at me and I almost vomited. I couldn't believe she smiled at me that way!"
The admiration is mutual. "Michael's a great guy," Jewel said after the show. "I relate to him because we both had kind of tough upbringings, and that can either make you bitter or it can make you stronger, and I think he's come out of it with compassion. That's nice to see."
Beginning Oct. 1, fans will have a chance to check out Grimm for themselves on the America's Got Talent Live tour. Beyond that, he's eager to get into the studio and record an album. "If people are thinking I'm gonna reinvent myself – it won't be that much," he says. "I'm definitely staying me."