The 62-year-old media mogul denied she and Graham are getting married in a tweet Monday after rumors circulated last week about their reported wedding.
"6 people who know me well have called today congratulating me or surprised they weren't invited to my wedding. It's not true!!" she told her 33.8 million followers.
Star magazine's Aug. 31 cover had declared that Winfrey and Graham were planning a "dream wedding" after 30 years of dating. Sources told the tabloid that Winfrey said "yes" after Graham jokingly brought up marriage.
"It suddenly dawned on her how Stedman has never asked her for anything or pressured her in any way," an insider said. "Oprah connected the dots and realized it was her turn to show how much she cares about what he wants."
"Everything with them is always very hush-hush, but the wedding will most likely be at Oprah's private estate in Maui which is picture-perfect for a romantic ceremony," the source added. "Oprah plans to fly everybody out to Maui at her own expense."
Winfrey and Graham have largely kept their relationship out of the spotlight during their many years of dating. The couple were engaged in 1992 but never married, although Winfrey reconsidered the prospect after Tina Turner's wedding in 2013.
"Tina was like, 'Oprah, you need to do this. You need to do it,'" she told Access Hollywood the same year. "And I was just thinking, 'Well, okay, would things really be different?' And no, I don't think so."
"If you ever interviewed [Stedman], he would tell you that had we married, we would not be together today. Because he's a traditional man and this is a very untraditional relationship," the star explained.
Winfrey is instead focused on her new OWN series, Queen Sugar, which she is co-executive producing with Selma director Ava DuVernay. The media mogul stunned in a fitted black dress at the show's premiere last week.