ET caught up with the newly engaged couple at the premiere of Roadside Attractions' Run the Race at the Egyptian Theatre in Los Angeles on Monday, where the former football star explained how he kept the exciting news a secret for so long.
"[I] started part of the planning from months ahead of time," Tebow, 31, explained, adding that he feels like he's a good secret keeper. "The problem is, once I felt like she started to get a clue, then I would, like, make up something else."
Nel-Peters chimed in, telling ET that Tebow planned everything "so delicately."
"I had absolutely no idea that it was gonna be that day," she confessed. "I mean, I definitely knew how I felt about him and how we felt about each other, so that wasn't a surprise, but I had no idea the proposal was gonna be that day."
"It was so, so special," she continued. "I had no idea, so, I mean, I felt like [he] did a really good job."
Tebow also said it "feels great" to be able to walk the red carpet with Nel-Peters as an engaged couple.
"We kind of do everything as an engaged couple, not just a red carpet," he said. "It doesn't matter if it was a blue carpet, we'd be enjoying it."
Tebow revealed last month via Instagram that he had popped the question to the 23-year-old former Miss Universe, sharing beautiful pics from the moment he got down on one knee.
"@demileighnp Thank you for saying YES and making me the happiest man in the world," he captioned the post. "You’re the love of my life, and I can't wait to spend the rest of my life with you."
The proposal came just a few months after Tebow confirmed he was dating Nel-Peters during an interview with ESPN last July. "She is a really special girl, and I am very lucky and blessed for her coming into my life," he gushed at the time. "I am usually very private with these things, but I am very thankful."