(Reuters) - Notre Dame football star Manti Te'o, whose on-field excellence after his grandmother and online girlfriend purportedly died made him a hero in the sports media, was the victim of a hoax because the girl never existed, the university said on Wednesday.

The girlfriend, who called herself Lennay Kekua and claimed to be a Stanford graduate, was merely an online persona who "ingratiated herself with Manti and then conspired with others to lead him to believe she had tragically died of leukemia," university spokesman Dennis Brown said in a statement.

Notre Dame Athletic Director Jack Swarbrick said the university learned of the hoax from Te'o on December 26. He answered questions forthrightly and private investigators uncovered several things that pointed to Te'o being a victim in the case.

"This was a very elaborate, very sophisticated hoax perpetrated for reasons we can't fully understand but had a certain cruelty at its core, based on the exchanges that we were able to see between some of the people who perpetrated it," Swarbrick told a news conference.

Notre Dame's statements came after the website Deadspin.com published a long expose under the headline "Blarney," alleging that Kekua was a hoax dreamed up by a friend of Te'o's.

"Manti Te'o did lose his grandmother this past fall. Annette Santiago died on September 11, 2012, at the age of 72, according to Social Security Administration records in Nexis," the website said.

"But there is no SSA record there of the death of Lennay Marie Kekua, that day or any other. Her passing, recounted so many times in the national media, produces no obituary or funeral announcement in Nexis, and no mention in the Stanford student newspaper."

Deadspin said photographs identified as Kekua and shown in online tributes and on TV news reports belonged to a living 22-year-old California woman of a different name who is not a Stanford graduate, has never had leukemia and has not met Te'o.

Te'o, an All-American linebacker and finalist for the Heisman Trophy, college football's top individual honor, acknowledged in a statement carried by ESPN.com and the Honolulu Star-Advertiser, that he had never met Kekua in person.

But he said Wednesday he had developed an emotional relationship with her and "maintained what I thought to be an authentic relationship by communicating frequently online and on the phone," according to the statement.

"To realize that I was the victim of what was apparently someone's sick joke and constant lies was, and is, painful and humiliating," Te'o said. Continued...