The Paper Roses hitmaker's 18-year-old Michael Bryan Blosil jumped to his death from the balcony of his Los Angeles apartment in 2010, following a long battle with depression.
Now the star, who was performing in Las Vegas at the time of his passing, has spoken about the darkest day of her life in new book The Key Is Love.
In an excerpt obtained by People magazine, she writes, "Exhausted from a non-stop week with shows, I was staying in a hotel room at the Flamingo that night with my daughter Rachael. My cell phone rang around 1:30am and it was a guard at the gate that leads into my neighborhood. He said, 'Someone is here from the coroner's office. They are coming to the Flamingo to see you.'
"My heart dropped to the floor. I said to Rachael, 'It has to be Michael'. 'No, Mom, no,' she said. 'I'll call him'. She dialed and redialed. She kept saying, 'Pick up, Michael. Be there.' The officer came to the door. He said, 'I'm very sorry to inform you that your son Michael committed suicide at 9:25 this evening. I thought someone had run a knife into my heart."
Michael struggled with multiple drug problems during his youth, and looking back Osmond admits she should have seen the warning signs he was headed towards destruction: "The week my son passed away, a friend from his drug-taking days decided to pay him a visit, along with some other friends. Michael agreed to go out with them.
"The next morning, Mike told his roommate that he had woken up under a highway overpass. He had no idea how he got there. He said he had not had any alcohol or taken any drugs on his own, but felt that one of the people in the car must have laced what he was drinking with something. Michael never told me of this incident, but two days before he died I heard a change in his voice over the phone and it frightened me.
"He sounded weary and said that he felt like he had no friends. I know now that my son was masking how deeply depressed he was."
And Osmond is still struggling to deal with the grief of losing her son, adding, "Not a day goes by that Michael isn't my first thought in the morning and my last before I fall asleep... It doesn't ever get better. I've come to accept that... (but) it's a choice to stay positive."