Video previews: http://abcnews.go.com/2020

"THE BIG LIE" ON "20/20" Airing Friday, June 8, 10 pm ET

What would it take to get you to tell a big lie? From an exclusive interview with a bride-to-be, who pretended to have cancer and duped her entire community, to a man who pretended to be his dead mother to collect social security, "20/20" reports on lies so big, it's hard to believe they are true. Also, Olympic gold gymnast Dominique Moceanu reveals for the first time on television a family secret hidden for two decades that would change her life forever. Anchored by John Qui�ones, "The Big Lie" airs on "20/20" FRIDAY, JUNE 8 (10:00-11:00 p.m., ET) on the ABC Television Network. Reports include:

Dominique Moceanu: Olympic gold medal gymnast Dominique Moceanu has written a memoir that exposes the underbelly of the sport that made her famous. She also reveals an extraordinary family secret hidden for two decades that would change her life forever. In an exclusive interview she candidly talks to John Qui�ones about Bela and Marta Karolyi, the coaches who honed her amazing talent, her parents, family, friends and her life today as a wife and mother.

Jerry Joseph: He was the basketball phenom destined to lead his new high school team to glory. But the mystery kid who showed up in Odessa, TX claiming to be a 15-year-old Haitian refugee was actually a mystery man � a 21-year-old drifter named Guerdwich Montimere looking for a new start� and a whole new life. Chris Cuomo has the first television interview with the hoop dreamer who was really an imposter.

Real-life Norman Bates Case: For six years, Thomas Parkin implanted a bizarre scheme that involved him impersonating his dead mother, fooling the federal and state governments, banks and the court system to collect on her Social Security payments and committing housing fraud. After his mother's death in 2003, Parkin lied about her birth date and social security number so she was never reported as dead. Authorities say, he was even caught on tape wearing a wig and dress at the Department of Motor Vehicles in order to renew her driver's license. Amy Robach talks to Parkin in his first interview since his conviction.

Cancer Bride: A community rallies around a bride-to-be, bravely facing terminal cancer by throwing her a wedding to remember. But the cancer story turns out to be a fraud -- a sick hoax by a woman in perfect health. And she's not the only cancer faker. Elizabeth Vargas has the first exclusive TV interview with the blushing bride and also exposes other cases of cancer liars.

David Sloan is executive producer of "20/20."