As he confessed to doping, lying and bullying others for years, Lance Armstrong remained calm and answered most of Oprah Winfrey’s questions matter-of-factly.

But when she asked him how he broke the truth to his oldest child, 13-year-old Luke, Armstrong cracked.

The disgraced cyclist became emotional in the second part of his lengthy interview with Winfrey Friday as he recounted telling Luke to stop defending him online and at school.

Armstrong said the painful conversation took place over the holidays.

“I want you to know that it’s true,” he told Luke after learning that his son was denying suggestions his dad ever used performance-enhancing drugs.

“I told Luke…don’t defend me anymore. Don’t,” Armstrong said, seemingly on the verge of tears as his eyes turned red.

At the beginning of the pre-taped interview, the first part of which aired Thursday night, Armstrong admitted to using banned substances and blood doping to win seven Tour de France titles. He had vigorously denied all allegations of doping for years, suing those who publicly spoke about his performance drug use.

Winfrey’s exclusive attracted 3.2 million viewers Thursday night, but Armstrong’s confession drew mostly negative responses from those he had lied to and viewers who expressed their thoughts on social media.

Armstrong said his older kids – Luke and 11-year-old twin daughters, Isabelle and Grace – have accepted his explanation. Luke told him that he still loved him, he said.

“He’s been remarkably calm and mature about this.”

Armstrong said he’s aware that his two youngest children, who are just toddlers, will eventually learn about his fall from grace.

His own mother has been a “wreck” since the scandal broke, he said, acknowledging that he’d hurt many people in his life.

Armstrong said it was his ex-wife Kristin, the mother of his first three kids, who told him: “The truth will set you free.”

He said he’d sought her blessing to return to professional cycling in 2009 and she made him promise he would do so without doping.

Armstrong insisted to Winfrey that his comeback was drug-free, although blood test results have suggested otherwise.

Earlier in the interview, Armstrong told Winfrey he thinks he deserves a chance to compete again in the future – even if it’s just running a marathon.

He was banned for life from sanctioned events and stripped of all Tour de France titles, after the U.S. Anti-Doping Agency concluded last October that he ran an elaborate doping scheme.

Armstrong said he doesn’t want to participate in another Tour, but would “love” to run the Chicago marathon when he’s 50 years old, for example.

“This may not be the most popular answer, but I think I deserve it,” he said.

Armstrong said being forced to leave the cancer charity he founded was the most humbling moment of his downfall.

He said stepping down from Livestrong, a charity inspired by his battle with testicular cancer in the 1990s, was more difficult that losing all of his corporate sponsors.

“That was the most humbling moment…The foundation was like my sixth child,” said the father of five.

Some legal experts say Armstrong’s admission may result in a litany of lawsuits against him and even prompt the U.S. government to consider reopening a criminal investigation.

A grand jury had heard testimony from Armstrong’s former teammates and associates, but federal prosecutors in Los Angeles announced almost a year ago that they were dropping their doping probe. No reason was given.

Armstrong has never spoken with federal authorities or testified before Congress on the matter, unlike some other professional athletes accused of using performance-enhancing drugs.

In the first part of Armstrong’s interview with Winfrey, he refused to implicate anyone else in what the USADA called an elaborate and sophisticated doping scheme.

He also denied, on two occasions, trying to pay off USADA to cover up the agency’s doping findings, as some have suggested.

On Thursday, the head of the USADA, Travis Tygart, said Armstrong’s confession “is a small step in the right direction but if he is sincere in his desire to correct his past mistakes he will testify under oath about the full extent of his doping activities."

Armstrong said his “ultimate crime” was betraying people who supported him and believed in him.

Asked what he would say to them, Armstrong replied: “I understand. You supported me forever  through all of this and believed and I lied to you. And I’m sorry.”

With files from The Associated Press