Official teaser from Teenage Newlyweds, viewers follow three couples building a life and future together - Credit FYI Television Network/Youtube

Sex is a “big mystery” for 21-year-old George, but that’s about to change dramatically when he marries his 18-year-old girlfriend Halie.

The young couple, who met during a mission for the Mormon church and decided to marry after two weeks, star in the new US series Teenage Newlyweds which follows the lead-up to their big day.

In a new clip of the premiere episode, George shares his fears about what will go down on the wedding night.

“We haven’t talked in depth. I’m kind of nervous for that,” George tells his friend when asked how he feels about “being intimate” with his bride for the first time.

“The only real sex talks I’ve had is with my friend who’s also getting married who’s never had sex.”

When his friend shares he’s “heard the first time’s a huge buzz kill”, George says: “Yeah, I heard sometimes they cry. Cause a lot of times it’s not what they’re expecting.”

Admitting that part of his faith is to not “participate in masturbation”, George added: “Honestly, sex is a big mystery. We talk about how it’s sacred a lot, like in church, but we don’t talk much about what it really is,” he adds.