A heartbroken Calvin Mitchell said Winfrey, 61, tried to adopt him as a boy, but then abandoned him as a teen, sending him spiraling into a deep depression.
A distraught Mitchell told RadarOnline.com: "I want to ask Oprah, 'Why did you leave me? Why did you leave me?'"
"I'm still empty," he confessed. "I'm still searching. I don't have closure to this. I just don't understand."
Mitchell claimed Winfrey turned her back on him after helping to raise him for five years when, as a "dumb" 17-year-old, he dropped out of the swanky private school she footed the bill for him to attend.
"I was young. I made a dumb decision, and Oprah wouldn't forgive me," said Calvin, now a 35-year-old truck driver. "I feel like what she did was wrong."
Mitchell recounted for RadarOnline.com how he met Oprah in 1992 when he was cast as an extra on the ABC-TV urban drama There Are No Children Here.
One day, the then-11 year old slipped past set security, picked a Diet Coke out of a cooler, and offered it to Winfrey, who was so touched that she offered the youngster a job as her so-called "personal bodyguard," revealed Mitchell.
After filming ended, Winfrey maintained contact with Mitchell — and even tried to make the boy part of her family.
"Oprah asked my mom if she could adopt me, and my mom denied her," he revealed.
Mitchell's mother, 56-year-old Eva Mitchell, told RadarOnline.com: "It felt strange because I felt if someone wanted to help me with my children, that's one thing. But to actually adopt one child knowing I have others? I couldn't allow her to separate my children."
Despite the refusal, Winfrey's partner Stedman Graham continued to treat Mitchell as one of his own.
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"He used to take me to Chicago Bulls games, and we went to the black rodeo that he hosted every year," Calvin told RadarOnline.com.
"We had a close relationship." Oprah and Stedman were like family to me."
Winfrey often gave the boy gifts, and Mitchell recalled that some came with messages attached, such as: "To my son Calvin, I love you."
When Mitchell became older, Winfrey paid for him to attend The Piney Woods School, a prestigious Christian-based boarding school for African Americans in Mississippi.
But Mitchell grew homesick and decided to drop out in his junior year, despite Winfrey's pleas that he stay and graduate.
"I just wanted to come home, and Oprah didn't understand that," Mitchell said.
"She told me, 'Calvin, just try to work it out. You can do it. Just hang in there.' She was trying to inspire me to do what was right. But even after the long pep talk she gave me, I still left."
It quickly became clear that Winfrey wasn't pleased with his decision, and she cut him out of her life, which sent him spiraling into depression and thoughts of suicide.
"By leaving school, I'd failed my whole family. I'd let everybody down," he told RadarOnline.com.
"But I thought Oprah and Stedman would still be a part of my life. At one point, it was like I'd lost my whole world."
"If it were my child, regardless of what that child did, they still would be a part of my life. Oprah and I had grown so tight that I thought she'd be a part of my life — forever."