Winfrey has defended the writer amid claims he fabricated details of his book A MILLION LITTLE PIECES, which Winfrey chose for her Book Club last year (05) - prompting a sales surge.
She has since discovered that Frey's story of substance abuse and recovery features information about a questionable drug rehab stint, which critics claim is inaccurate.
During a taped episode of her show, which airs in America today (26JAN06), Oprah told Frey, "It is difficult for me to talk to you because I really feel duped... I feel that you betrayed millions of readers."
Winfrey even defended Frey, 36, when he appeared on a recent LARRY KING LIVE show on CNN after scandal website The Smoking Gun exposed the author as a reported liar.
The media mogul has since been widely criticised and now admits she regrets standing up for Frey on King's show, stating, "I left the impression that the truth is not important."
Frey has acknowledged he embellished parts of the book, and he told Winfrey on her show, "I made a mistake."
Bosses at Frey's publishers, Doubleday, have insisted the writer pens a brief author's note for future editions of his memoir, explaining some details are embellished.