Rock Center with Brian Williams By Jessica Hopper Rock Center Mimi Alford is speaking publicly for the first time about the secret she's held for half a century. Alford claims that she had an 18-month-long affair with President John F. Kennedy when she was a White House intern. "I think when you keep a secret and when you keep silent about something, you do it because you think it's keeping you safe, but in fact, it's deadly," Alford told Meredith Vieira in an exclusive interview scheduled to air Wednesday on NBC's Rock Center with Brian Williams. In 1962, a 19-year-old Alford spent her summer in Washington, D.C., interning in the White House press office. She had just finished her freshman year at Wheaton College in Massachusetts. Four days into her internship, Alford claims that JFK aide, David Powers, invited her to go swimming in the White House pool. Alford was surprised when the 45-year-old president joined her and two others in the pool. "It really didn't seem unnatural, just because everybody was friendly and I went back to work afterwards," Alford said. No one said anything. Later that day, she says she received another call to visit the private floors of the White House. The naïve teenager didn't question the president's intentions when he asked to take her on a tour of the White House. The president came over to me and asked me if I'd like to take a tour of the second floor of the White House and see some of the rooms that had been redecorated. The last room that we went into was the bedroom and we walked into the bedroom and it was a beautiful room...I learned later that it was Mrs. Kennedy's bedroom," Alford said. Alford says that she lost her virginity to the president in the first lady's bedroom. In her soon to be released memoir, Once Upon a Secret My Affair with President John F. Kennedy and its Aftermath, Alford described her first sexual encounter with the president writing that, "I wouldn't describe what happened that night as making love, but I wouldn't call it nonconsensual either." When asked if she felt overpowered by Kennedy, she told Vieira, "I think overpowered in the sense that he was the president. He was this unbelievably handsome man, 45 years old, overpowered in the fact that he had chosen me...and taken me on this tour. That's what I mean by being overpowered by the whole situation. Not overpowered physically that someone had grabbed me and done this to me and made me do something that I wasn't really willing to do, because I really think I was willing to do it. Alford emphasized to Vieira that if she had told the president no, he would have stopped. The affair continued for 18 months even after Alford returned to college. "I think I was under the aura of, I had just a little bit of second thoughts, not enough to keep me from going back," said Alford of the affair's beginnings. While interning, Alford would sometimes travel with the president. When she returned to college, he'd have arrangements made for her to come visit him. Sometimes, a limo would pick her up and take her to the airport to fly to Washington, D.C. Alford remembers doing homework in the limo as she headed to meet the president. I should have felt guilty. He was married to Mrs. Kennedy, but I didn't at the time feel guilty," Alford said. Looking back now, Alford says that she realizes she was at Kennedy's beck and call. I think that's probably partly what makes me feel sad when I look back. It made me feel very special," Alford said. Alford described Kennedy as "boyish" and "shy" around her. I'm not going to say he loved me, but I think he did like me a lot. He cared about me," she said. Just the way he was, the way he smiled with me. I feel that he did. I feel that he actually cared about me. When pressed by Vieira about whether she really believes that Kennedy had genuine feelings for her or if believing that is simply a way for her to comfort herself all these years later, Alford said, "I think it's a little bit of both." Now 68, Alford's soon to be released memoir shares explicit details about the affair, including a claim that the president encouraged her to have sexual relations with at least one other person at the White House. Alford says that keeping the affair secret was more damaging than the affair itself. She said that it affected her relationships and contributed to the demise of her first marriage. Alford was first publicly outed in 2003 when historian Robert Dallek wrote 37 words about an unnamed intern who had an affair with Kennedy in his biography of Kennedy called An Unfinished Life. The New York Daily News identified her and Alford issued a simple written statement confirming her secret relationship. She faded into obscurity, but said that the secret eventually became too much to hold inside. "It's not so much that I feel that I'm exposing myself, it's that I'm really unburdening myself, it was a very difficult thing for me to do," Alford said. In fact, most mornings when I woke up I thought I don't want to get up and write this book, I want to hide under the covers. Editor's Note: Meredith Vieira's exclusive interview with Mimi Alford airs Wednesday, Feb. 8 at 9pm/8c on NBC's Rock Center with Brian Williams. Vieira talks to Alford at length in the author's first candid interview.