It's been more than two decades since Brittny Gastineau's father Mark, the legendary New York Jets player, left Brittny's mom Lisa for actress Brigitte Nielsen. But it wasn't until last week that Brittny met the fruit of that union: her half-brother Killian Marcus Gastineau, who's now 20.
Brittny had never before seen or spoken to Killian, who lives in Italy and works at a wine and champagne company. "I've always known I have a half-brother, I was told as a kid, but he was totally off the radar. It was like he didn't exist," Brittny tells PEOPLE.