Feb. 10, 2012 — -- Karen Gravano was 10 the first time she suspected her father was a killer.
She was on her way to ask her dad's permission to go to a sleepover with her fifth-grade friends when she caught him in his bedroom with a gun.
"The door was closed a little bit," she said. "And when I opened it, he turned real quick, and I [saw] him tuck a gun into the back of his pants. And I looked at it for a minute, and, um, I didn't ask. And he looked over at me, and he says, 'Don't you knock?'"
One of her father's rivals was fatally shot that night.
Gravano's father is none other than Sammy "The Bull" Gravano, the infamous mob underboss who killed 19 people before cooperating with the government in the takedown of the Gambino crime family and other crime families. Karen Gravano now stars in the VH1 reality-TV show "Mob Wives" and has written a memoir of her life, "Mob Daughter," that will be released Feb. 14. (Read an excerpt of "Mob Daughter" here.)
In an interview with "20/20," Gravano, 39, said there were certain perks to being the daughter of The Bull, especially in the Staten Island, N.Y., neighborhood where she was raised.
"You can walk in a restaurant and you were, you know, given the best table," she said. "Most of the time, your check was picked up. Gangsters are looked up to, especially in the neighborhoods that we grew up in."
One of the guests at her Sweet 16 birthday party was John Gotti, her father's mobster boss, who came bearing a cash gift.
"I walked over and my father said, 'Say hello to Uncle John.' And I said hello to Uncle John, and he gave me an envelope," she said. "And in the envelope was, you know, 10 hundred dollar bills."
Gotti's presence at the party was like a badge of honor and earned her respect in the neighborhood.
"When I went back to school, people were like, you know, "I heard John Gotti was at your party, you little Mafia Princess,'" she said.
As she grew older, the Mafia Princess -- a nickname that Gravano says she finds offensive -- turned into a business owner, thanks to her dad.
Sammy Gravano bought his daughter a flower shop for her high school graduation. And thanks to The Bull's connections, business was excellent.
"It was a booming business overnight," Karen Gravano said. "Gangsters love to send flowers, I guess."
But all the flowers in the world couldn't make up for the sense of betrayal Karen Gravano felt one autumn day in 1991. She was 19 when her father told her and her family he would begin helping the government pursue charges against his mob buddies, including boss Gotti. In exchange for his cooperation, Gravano was not prosecuted for his 19 murders and instead was convicted of a lesser charge that resulted in a jail sentence of a few years.
Karen Gravano responded with anger to her father's bombshell.
"Everything he taught me in my life [was], 'You never tell,'" she said. "I felt like the life that I grew up in was ripped out from underneath me."
Watch the full story on "20/20" Friday at 10 p.m. ET.