The duo performed "The Way You Make Me Feel" together for Jackson's 30th Anniversary Celebration, which aired on CBS in 2001.
"I was so excited to see his show in London," Spears said in a statement today. "We were going to be on tour in Europe at the same time and I was going to fly in to see him. He has been an inspiration throughout my entire life and I'm devastated he's gone!"
"I can't find the words right now to express how deeply saddened I am by Michael's passing," the pop-R&B hitmaker wrote. "We have lost a genius and a true ambassador of not only Pop music but of all music. He has been an inspiration to multiple generations and I will always cherish the moments I shared with him on stage and all of the things I learned about music from him and the time we spent together. My heart goes out to his family and loved ones."
And the proof of Jackson's tremendous influence on the next generation of music makers didn't stop there.
Beyoncé called Jackson's death a "tragic loss" on a "terrible day."
"The incomparable Michael Jackson has made a bigger impact on music than any other artist in the history of music," the 27-year-old singer said. "He was magic. He was what we all strive to be. He will always be the King of Pop!
"Life is not about how many breaths you take, but about how many moments in life that take your breath away. For anyone who has ever seen, felt, or heard his art, we are all honored to have been alive in this generation to experience the magic of Michael Jackson. I love you Michael."
Usher, who shared a stage with Jackson once, is also "deeply saddened" by the loss.
"May God cover you Michael. We all lift your name up in prayer. I pray for the entire JACKSON family particularly Michael's mother, children and all his fans that loved him so much," Usher wrote in a statement released by his rep.
"I would not be the artist, performer, and philanthropist I am today without the influence of Michael. I have great admiration and respect for Him and I'm so thankful I had the opportunity to meet and perform with such a great entertainer, who in so many ways, transcended the culture. He broke barriers, he changed radio formats! With music, he made it possible for people like Oprah Winfrey and Barack Obama to impact the mainstream world. His legacy is unparalleled. Michael Jackson will never be forgotten."
Meanwhile, Sheryl Crow actually worked for Jackson, having landed a spot as a backup singer on his Bad tour in the late 1980s.
"His was a rare talent that we witness once in a lifetime," she said. "One who makes such an indelible mark that for generations singers and dancers attribute him as inspiration. I had the great privilege of watching him every night doing what he did best—entertain. I am grateful to have known him for the 2 years I worked for him and will mourn his loss with his many millions of fans across the world."
From child star to music icon—reflect on Michael Jackson's life with our collection of photos.