Osmond is speaking out for the first time about the day Blosil died. Today, the entertainment icon tearfully told talk show host Oprah Winfrey about the very last conversation she had with her son.
Son to Mom: 'I Have No Friends'
The last time they spoke, Blosil expressed despair.
"When I heard him say to me, I have no friends, it brought back when I went through depression, because you really feel so alone," Osmond said.
"I'm not a depressed person, but I understand that place, that darkness," she said, referring to post-partum depression.
Osmond became emotional as she talked about that conversation.
"I told him, I said, 'Mike, I'm gonna be there Monday and it's gonna be OK.' But depression doesn't wait 'til Monday," she said.
It was Friday, Feb. 26, when Blosil jumped to his death from the roof of his apartment building in Los Angeles.
Blosil, a first-year student at the Fashion Institute of Design and Merchandising, had battled with substance abuse and depression following his parents' divorce in 2007.
He entered rehab after the divorce.
Speaking of her son's struggles to talk show host Larry King that year, Osmond said Blosil was "dealing with a lot. He's one of my kids. He's dealing with adoption issues, all kinds of things right now."
Blosil was one of five children adopted by the star.
Osmond Says Stage Is 'Safe Place'
One day after Blosil's funeral, less than two weeks of her son's death, Osmond made an emotional return to her Las Vegas show with her brother, Donny Osmond.
"The way Osmonds survive is we keep singing, and I know my son would want that," she told the audience at one of her performances.
Osmond called the stage her "safe place."
"It doesn't scare me, like I guess it scares some people. And I knew that if I didn't get back on stage, that I may never get back on stage," she said.
The twice-divorced single mother of seven has struggled to stay strong since Blosil's death.
"I've been through some tough things in my life. This is probably the hardest thing I've been through," Osmond said.
Asked if she ever thought about what she could have done differently to help her son, she said: "I think there's always 'what ifs.'
"What if I had just put him on a plane and said come be with me, or gone there?" she asked. "I think if you life in 'what ifs' ... you stop living."
Osmond and her brother, Donny, are doing a Christmas special on Broadway for 21 days in December.
ABC News' Kelly Hagan and Katie Escherich contributed to this report.