The latest addition to NBC’s weeknight lineup is among one of the most highly anticipated new series to fall TV. “This is Us” premiered Monday to a large audience, proving that it was worth every bit of buzz by unveiling a shocking twist no one could have seen coming.

The show centers around five people — one couple, two siblings and a big wig trying to discover his roots. During the inaugural episode of Season 1 viewers learn that each of the main characters are more connected than they may seem on the surface. Kevin (Justin Hartley) and Kate (Chrissy Metz) are two-thirds of a set of triplets. Their brother, however, died at birth. During Season 1, episode 1 of “This is Us” viewers learn that Randall (Sterling K. Brown) — who is on a quest to find his biological father — is their adopted brother. Jack (Milo Ventimiglia) and Rebecca (Mandy Moore) are the parents of this group, shown 36 years in the past preparing for the birth of their triplets. During a premiere party in Los Angeles, Many Moore opened up about keeping the story under wraps, expressing her deep thanks to everyone and anyone that knew what was coming.

“We’re all very grateful that people have kept this secret,” she told USA Today on Monday. “It’s nice to celebrate with the entire cast and have the shared experience.”

When asked about the decision to include a twist, “This is Us” creator Dan Fogelman told Entertainment Weekly it was entirely intentional. He and the writers were careful not to give anything away during initial character introductions, a fact he remains proud of. Fogelman said there were a lot of decisions showrunners had to make to ensure that lighting or small details didn’t give away the differences in time.

“It was always designed to be exactly where it is. It was written as such. Looking back on the pilot, obviously the locations are very well-disguised. John and Glenn [Requa and Ficcara respectively] did a brilliant, brilliant job of making everything correct,” Fogelman said. “Even the lighting palette of the rest of the show makes it so that segment doesn’t stand out but still looks very much of the time.”

At the opening of “This is Us,” viewers learn that Jack, Kate, Randall and Kevin are all celebrating their 36th birthdays. Each appear, at first, to be strangers living in the same time period. Jack is a Pittsburgh, Pennsylvania, dweller who, in addition to getting a year older, is about to enter into fatherhood. In keeping with tradition, Rebecca reluctantly agrees to do a sexy birthday dance for her husband. Despite her hesitance, things are going swimmingly — until her water breaks.

Viewers are then introduced to Kate, who is standing before a full refrigerator in which the tastiest, but most unhealthy, foods are marked with notes urging her to “Throw this crap out.” She has both food and body image issues, which will play a large role in her character development throughout the season. While she stresses over shedding a few ounces before her birthday bash, Randall — a high-profile businessman — with a wife and two children on a quest to find his birth father.

Lastly we meet Kevin, a handsome, fit, sitcom actor questioning his career path. During one particular scene the “Man-ny” star is seen struggling to pin down where exactly he went wrong, when he’s interrupted by a call from his sister who turns out to Kate. Struggling with a crisis of her own, Kevin agrees to come over and console his twin.

Once together, Kevin and Kate muse about their changing age and their stations in life. Kate reveals that she just wants to be more like their parents, balancing a family and a career. She worries that her weight is the reason she is still unwed. “This is Us” then cuts back to Jack and Rebecca, who have arrived at the hospital. Naturally, her doctor has suffered a medical emergency of his own and will be unable to help her deliver her three children. To make matters worse, the infants are not in an ideal position.

While they get acquainted with a new doctor, Randall and Beth (Susan Kelechi Watson) are cheering on their children during their respective soccer games. The business executive opens up to his wife about his parents, revealing that he doesn’t know who his father is and has been searching for him. Randall further shocks Beth by telling her that he’s found the man he believes to be his dad and wants to seek him out. He is unsure why he chose to look for his father, but decides to go through with meeting him anyway. Randall shows up on his father, William’s (Ron Cephas Jones), doorstep and is reluctantly invited in. The absentee father makes no excuses about his behavior and is apologetic. He tells Randall that he’s cleaned up his act and is invited to meet the kids. One hang up with this heartwarming reunion — William’s time on earth is limited.

Kate has decided to take matters of weight into her own hands, attending a support group for people who struggle with their size. There she meets Toby (Chris Sullivan) and her life is turned upside down. Toby asks whether she wants to be “far friends” with him and doubts her ability to lose weight. She immediately shuts down his advances, telling him there’s no room in her life for a fat guy.

“I guess I’ll lose the weight then,” he says.

Back at the hospital Jack, Rebecca and Dr. K are bracing for whatever will come. The obstetrician is hopeful going into the delivery. Rebecca welcomes her first of three children — a boy — without incident. Jack is removed from the birthing room and the trouble begins. When Dr. K steps into the waiting room to face Jack again, his demeanor has changed. Something is clearly wrong. He reveals to the first time father that one of his three kids did not make it due to an umbilical cord issue, which weighs heavy on Jack and viewers.

“This is Us” airs Tuesdays at 10 p.m. EDT on NBC.

“This is Us” “This is Us” premiere revealed a plot twist no one could have predicted. Photo: NBC