In part one of his no-holds-barred interview with Oprah Winfrey, Lance Armstrong admitted to using banned substances to enhance his cycling performance. "Oprah and Lance Armstrong: The Worldwide Exclusive" continues January 18 on OWN and Oprah.com. In this clip, Armstrong talks to Oprah about the moment he told his 13-year-old son, Luke, the truth. Watch part two of Oprah's interview with Lance Armstrong on Friday, Jan. 18, starting at 9 p.m. ET on OWN.