Jan. 23, 2013 -- Manti Te'o briefly lied to the media and the public after discovering his online girlfriend did not exist and was a part of an elaborate hoax, he admitted in an exclusive interview with ABC News' Katie Couric.

The star Notre Dame linebacker, who has been hounded by the reporters since the story broke Jan. 16, told Couric in a taped interview Tuesday that he was not lying up until December. Te'o said he was duped into believing his online girlfriend, Lennay Kekua, died of cancer.

"You stuck to the script. And you knew that something was amiss, Manti," Couric said.

Te'o found out that Kekua was a hoax on Dec. 6, but on Dec. 8 he again publicly mentioned his girlfriend. The remark came as Te'o was a finalist for the Heisman Trophy, the award for the best college football player in the country. Te'o was eventually a runner-up for the trophy.

"Katie, put yourself in my situation. I, my whole world told me that she died on Sept. 12. Everybody knew that. This girl, who I committed myself to, died on Sept. 12," Te'o said.

"Now I get a phone call on Dec. 6, saying that she's alive and then I'm going be put on national TV two days later. And to ask me about the same question. You know, what would you do?" Te'o said.

See more exclusive previews tonight on "World News With Diane Sawyer" and "Nightline." Watch Katie Couric's interview with Manti Te'o and his parents Thursday. Check your local listings or click here for online station finder.

Te'o, 21, was joined by his parents, Brian and Ottilia, in the interview.

"Now many people writing about this are calling your son a liar. They are saying he manipulated the truth, really for personal gain," Couric said to Te'o's father.

"People can speculate about what they think he is. I've known him 21 years of his life. And he's not a liar. He's a kid," Brian Te'o said with tears in his eyes.

Click here for a who's who in the Manti Te'o case.

Diane O'Meara told NBC's "Today" show Tuesday that she was used as the "face" of the Twitter account of Manti Te'o's online girlfriend without her knowledge or consent.

O'Meara said that Ronaiah Tuiasosopo used pictures of her without her knowledge in creating Kekua.

"I've never met Manti Te'o in my entire life. I've never spoke with him. I've never exchanged words with him," O'Meara said Tuesday.

The 23-year-old marketing executive went to high school in California with Tuiasosopo, but she says they're not close. Tuiasosopo called to apologize the day Deadspin.com broke the hoax story, she said.

Timeline of Manti Te'o girlfriend hoax story

In an interview with ESPN last week, Te'o said he had received a Twitter message from Tuiasosopo apologizing for the hoax.

The Hawaiian also spoke to Tuiasosopo on the phone the day the Deadspin report came out, according to ESPN.com. He found out that "two guys and a girl are responsible for the whole thing," he said.

But he did not know the identities of the other individuals involved, other than the man he says was Tuiasosopo.

Tuiasosopo, a 22-year-old resident of California, has not admitted involvement publicly. Tuiasosopo graduated from Paraclete High School in Lancaster, Calif., in 2007 and has posted dozens of videos online signing Christian songs.

Those who knew him say he was a devout Christian and a good athlete. His former football coach Jon Flemming described him as gregarious, and from a "good loving family." Flemming said Tuiasosopo is the kind of guy who gives you a hug when he sees people he knows.

"He's doing good. Wishing everyone would go away," Flemming told ABC News Wednesday after a recent correspondence with Tuiasosopo.

Flemming said Tuiasosopo is "somebody I'd want my kid to grow up like. He's responsible, respectful, disciplined, dedicated."

Tessi Toluta'u, a Polynesian beauty queen, told ABC News this weekend that "Lennay Kekua" reached out to her in 2008 about entering pageants.

When visiting Los Angeles in 2009, Toluta'u was supposed to meet Kekua, but she failed to appear. Tuiasosopo met Toluta'u instead.

"[It's a] sick joke that went way too far," Toluta'u said.