"Yes, I have filed for divorce," the 45-year-old Oscar-winning actress said in an interview. "I'm sad and I am scared."
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Bullock and James, 41, began the adoption process four years ago, the report said, and brought 3 1/2-month-old Louis Bardo Bullock home in January but decided to keep the news to themselves until after the Oscars. The baby was born in New Orleans, the story said.
James and Bullock separated in March after five years of marriage, following reports that James had been unfaithful.
Bullock won the Oscar for best actress for her role in the blockbuster hit "The Blind Side" on March 7. Within days of her win, the cheating allegations became public and Bullock went into seclusion.
The motorcycle mogul publicly apologized to Bullock and his children, Sunny, 6; Jesse Jr., 12; and Chandler, 15.
RELATED VIDEO: Bullock reveals divorce, adopted son
He recently returned home after a 30-day stay in a treatment facility where he sought help for "personal issues," the story on People's website said.
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When asked about whether James had cheated, Bullock said she "had no idea about anything."
"I did the only thing I could do, and that was to pack enough clothes to live on, get all of Louis' things and get out of town. My main concern was Louis."
Bullock didn't discuss details of the adoption to protect her son's privacy.
When asked whether James will have any formal parenting role, she replied: "I will be adopting as a single parent. Anything else will be taken day by day."
She said of her relationship with Jesse's three children: "I don't want to know what life is like without those kids. ... Whatever we need to do, in the healthiest way, we are going to be co-parenting."