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As Marie Osmond left the Flamingo Las Vegas stage to the fading roar of a sold-out crowd on Feb. 26, she had no idea her world was about to change forever. "She was packing up and about to go home," says Donny & Marie producer Chip Lightman, "when she got the news." Her 18-year-old son, Michael Bryan, had jumped to his death from the eighth-floor balcony of his Los Angeles apartment. When Lightman arrived an hour later, he says, "No one could have said anything to console her. She's absolutely devastated."

Now the large and loving Osmond clan, including brother Donny, 52, has rallied around Marie, 50, and her seven surviving children (grade-school age to 26) at their Las Vegas-area home. "She's a mess," says a family friend. Adds her longtime assistant Darla Sperry: "She's grieving the loss of her sweet Michael; it would be so unbearable if she weren't surrounded by family and friends. He [was] a good boy, an angel."

Which is why those who knew and loved Michael, a first-year student at the Fashion Institute of Design & Merchandising, are struggling to make sense of his tragic death. (L.A. County Coroner Assistant Chief Ed Winter says the teen left a suicide note and sent a final text message to a female friend; neither has been made public, and toxicology results will not be available for weeks.) Though he had gone to rehab for substance abuse in 2007-he "got into the wrong crowd," Donny said at the time-he had been thriving since then. "I couldn't be more proud of him," Marie told PEOPLE last year, boasting about her son's "3.9 GPA." In October she tweeted about "parents day" at FIDM and wrote, "Wow, I'm proud of that kid! He really took charge of his future."

That included giving himself a new last name. According to a family friend, Michael (who, like four of his siblings, was adopted) legally changed his last name from Blosil to Bryan. The family friend says Michael was estranged from his father, Brian Blosil, 57, a music producer whom Osmond divorced in 2007 after 20 years of marriage. (Blosil declined to speak to PEOPLE about his son's passing.) One of Michael's close friends in Orem, Utah-where the family lived until they moved to Nevada in 2008-says he "was happy" and "loved" L.A., where he "had a lot of friends." They spoke just two days before his death, and the pal says, "It didn't seem like anything was wrong. He seemed like Michael to me."

That her son was battling his own private despair must be doubly painful for Osmond, who suffered postpartum depression after the birth of her son Matthew in 1999. In her 2001 memoir Behind the Smile, she wrote about making mistakes as a mom but wanting to spare her kids from "the feeling of not being able to get out of bed in the morning because of debilitating depression." Says the family friend: "Marie knew Michael was troubled, but I don't think she ever thought he would take his life."

The Michael everyone will remember was a talented musician in a close-knit family. As a child, he and his siblings logged a lot of time on the road with Mom. "We had a great time, all crowded into one bus, traveling to a new city every day and performing at night," Osmond wrote in her 2009 memoir, Might As Well Laugh About It Now. Michael had played drums in his mother's 2006 Christmas show, and at home in Utah was in a metal-inspired band, Without a Trace. Marie attended many of his gigs and transported equipment in her car. Whenever they were together, "she would always tell him 'I love you' when he was leaving," says his pal, "and tell him to be safe."

Though Michael's rehab stint coincided with his mother's turn on Dancing with the Stars, she "visited Michael so many times," says her partner Jonathan Roberts. Adds pal Leeza Gibbons: "I've never seen a more dedicated mother." Just on Jan. 2, Osmond said via Twitter, "Hanging out with my son, before he goes back to college. I want to go take a class or two. Think he would mind???"

In the wake of the tragedy, Osmond canceled her Las Vegas show for a week. "She said, 'I need to be with the kids completely,'" explains Lightman, adding that the Osmonds' show-will-go-on work ethic means she may return after Michael's Utah funeral. Her loved ones will be there for her every step of the way. "Her family will do what it always does: pray and pull together," says Gibbons. "Her strength and faith will be called upon now like never before."