In looking back at her "surreal" time with the King of Pop, Sheryl said it would have been difficult to imagine Jackson becoming an old man.
"For a moment there, I kind hoped that he'd staged his own getaway," Sheryl told CNN's Anderson Cooper during a phone interview Thursday night after news broke that Jackson died at age 50. "He's got a lot of gigs coming up and the pressure of that, and I thought maybe he'd just staged a getaway. And when the news really started trickling in…it's just, it's makes my heart sick."
Sheryl explained that she found it hard to foresee Jackson aging into his golden years.
"It's tragic at 50 he's gone," Sheryl said. "But did we ever think he was going to grow to be an old man before our eyes? It would have almost been too surreal."
Though Sheryl's heart aches with his passing, she said she looks back on her time spent with the pop star with great joy.
"I can't explain to you how much of a life [changing experience] it was for me to sing with him. There's no way to express how amazingly talented this person was, because, not only had he been doing that quality of work his whole life, but he created dance moves that nobody had ever seen before, and to create something that no one has ever imagined is quite a gift," she continued, adding, "He has literally inspired Usher and Justin Timberlake and every young artist who has come along."
She describes her time spent on Jackson's "Bad" tour as unlike anything she'd ever experienced, especially the time spent alone with the pop star.
"It was really surreal. I was lucky in that I got to hang out with him on a number of occasions by myself," she recalled, "He invited me to his hotel room in Tokyo and we watched 'Amos & Andy' videos and the movie 'Shane,' just completely unexpected. He was funny, he had a big laugh, he loved practical joking and I can remember vividly going to Disneyland and going on a ride with him and he wouldn't let the ride stop and by the end of it I was just absolutely ill. And he thought that was the funniest things he'd ever seen."
Sheryl said that she worried about the pressure mounting on Jackson surrounding his 50 sold-out shows at London's O2 Arena, which were to begin in July.
"I think he felt pressure in every way. He had been under real scrutiny for the last 10 to 15 years. He'd been in real financial trouble. This was sort of a comeback for him. And that's got to be an immense amount of pressure," she told Anderson, adding, "I'm going to mourn his loss just like millions and millions of other fans out there, and I'm grateful for a brief moment in my life that I got to stand on stage nightly and watch him sing 'Human Nature' and 'Billie Jean' and do those moves and sing those incredible melodies, that were original to him… I'm sad and grateful at the same time."