The talk show queen filmed the candid chat with Armstrong on Monday and later called it "the biggest interview I've ever done" after he reportedly confessed to using performance-enhancing drugs.
Now Winfrey's best friend Gayle King reveals the TV star landed the job at the last minute and rushed to come up with 112 pressing questions for the athlete, who was stripped of his seven Tour de France titles over the doping scandal.
TV anchor King tells the New York Daily News:"It all just came together for her within the past week. She was really into it. Because it came together so quickly, she knew what an important interview it was for her. She knew the expectation was, 'Oh, Oprah's gonna throw him puffballs (easy questions).' She also knew that she was going to have to ask the hard questions.
"And it's not that she's not capable of it; she wanted to make sure she was thoroughly prepared. She wants people to judge for themselves, but it is a big get and she knew everybody wanted it, and she is happy with it. When people talk about this interview on Friday, they're gonna say, 'Wow, Oprah really knocked it out of the park.'"
Winfrey's interview with Armstrong is due to air on her US network OWN in two parts on Thursday and Friday.