A complicated love triangle... turns deadly.

True crime fans will remember the riveting true story of young Southern California military wife and newlywed, Erin Corwin, who vanished in 2014 after leaving home for Joshua Tree National Park. She was later found murdered in the desert.

Sadie Calvano plays Corwin and shared how naive Erin was at just 19-years-old.

"She's excited and in love, and goes to this marine base, and it's not at all what she imagined," Calvano said.

In their investigation, detectives learn that Erin had an affair with Marine Christopher Lee, played by Tom Stevens. Since Erin was pregnant during her mysterious disappearance, her family questions the paternity of Erin's baby.

"[Christopher] gets put at a crossroads when she gets pregnant, that he makes a choice that is fueled entirely by his sickness," Stevens said.

Erin's husband, Jon Corwin, immediately gets caught in the middle of the investigation and the tragedy. Played by Evan Roderick, the star revealed the trauma Jon endured during his wife's murder.

"It's not just adultery. He's sad about that and then he's screwed up, because she's gone and he doesn't know what happened. Not to mention, the police and the FBI think it's him," Roderick said.

All will be revealed when Secrets of a Marine's Wife premieres Saturday, June 19th, on Lifetime.