Young Rock,” an upcoming NBC comedy about the formative years of Dwayne Johsnon, continues to round out its ensemble.

Actor Lexie Duncan has been cast as a high-school sweetheart for the superstar during his teens, where she will play opposite Bradley Constant (the 15-year-old version of Johnson).

She’s set to play Karen, a popular, charismatic, high-school girl with dreams of attending Barbizon beauty school. Constant’s character catches her eye, and they begin dating in the idyllic town of Bethlehem, Pennsylvania.

Duncan, who hails from musical theater and marks her primetime debut in this role, is repped by Luber Roklin, Active Artists Management and The Initiative Group.

The series comes from Johnson’s company Seven Bucks and “Fresh Off the Boat” creator and executive producer Nahnatchka Khan, who wrote the pilot with collaborator Jeff Chiang.

Johnson, the star of the “Fast and the Furious” spinoff franchise “Hobbs & Shaw,” as well as the upcoming Disney adventure “Jungle Cruise,” will be seen at three ages in the series: at 10, to be played by Adrian Groulx; at age 15 by Constant; and from 18-20 by “Marco Polo” star Uli Latukeful when Johnson is recruited to play football on a scholarship at the University of Miami.

Seven Bucks’ Dany Garcia, Hiram Garcia, and Brian Gewirtz are executive producing, as well as Jennifer Carreras of Khan’s Fierce Baby Productions. The project is set up at Universal Television, where Khan is engaged in an overall deal. Jeffrey Walker is on board as producer, director and co-EP. The series is set for debut sometime in 2021.