Saying she felt "duped," Oprah Winfrey challenged author James Frey on the accuracy of his book, "A Million Little Pieces," which Winfrey's book club helped propel to bestseller status, Bloomberg News reported Jan. 26.

Multiple critics have attacked Frey's memoir about addiction and recovery -- which last year was the second-biggest seller in the U.S. behind "Harry Potter and the Half-Blood Prince" -- as depicting events that were wildly embellished or simply never happened. Frey initially dismissed his critics, and Winfrey called during the author's recent appearance on 'Larry King Live' to defend the book.

This week, however, Frey said of his critics: "I think most of what they wrote is pretty accurate." Winfrey hit Frey with a series of questions about disputed passages in the book, including a since-disproven claim that Frey had spent an extended stint in jail, and Frey's story about his girlfriend killing herself the day he left addiction treatment.

"It is difficult for me to talk to you because I really feel duped," said Winfrey, who said she regretted having called Larry King to defend Frey. "As I sit here today, I don't know what is truth and I don't know what isn't," she added.

Winfrey asked why Frey didn't just call his work fiction instead of nonfiction. "I don't think it is a novel," he replied. "I still think it's a memoir." Winfrey replied that she felt "conned" by Frey, who she accused of lying in the book.