9-1-1: Lone Star: First Look Photos of Grace and Her Sisters Feature a McClain Family Reunion (Exclusive)

When 9-1-1: Lone Star co-creator and showrunner Tim Minear approached actress Sierra McClain about an upcoming episode that would expand the immediate family of Grace Ryder, they both had a clear idea of who should play her character's sisters: her real-life sisters, Lauryn and China Anne McClain.

"Having my sisters come to Lone Star was something I'd wanted to do for a while," Sierra told TV Guide in an exclusive first look at the chapter airing April 18. "Then, during one of me and Tim's beginning-of-the-season chats, he pulled the idea right out of my mouth! I certainly didn't think it would happen as soon as it did, but before I knew it, he was sharing storyline possibilities with me. I've lived with Grace for four years now, so being able to introduce this aspect of her family life that's so similar to mine, in such a personal way, really helps make Grace even more real to me."

In next week's episode, titled "Open," Grace struggles with confronting her father, Benjamin (William Allen Young), over his past infidelity. But while babysitting Charlie one day with his wife, Denice (Barbara Eve Harris), Benjamin suffers a heart attack, forcing Grace and her sisters, Lisa (China Anne) and Ashley (Lauryn), to come together in his hour of need.

9-1-1: Lone Star's Jim Parrack Weighs In on That New Baby Shocker

As viewers might recall from the "Difficult Conversations" episode of the second season, Grace's husband, Judd (Jim Parrack), found his father-in-law suffering from hypoglycemic shock while "fooling around" with another woman — who was most definitely not his mother-in-law — in a hotel room. While Judd struggled with whether or not to tell his wife, Grace learned of her father's actions by the end of the hour. But she decided against telling her mother, and the storyline has been a loose end on the show for years — until now.

The episode will reunite the tight-knit McClain sisters, who form the girl group Thriii, for the first time on-screen since working together briefly in China Anne's Disney Channel musical sitcom A.N.T. Farm, which ran from 2011 to 2014. They made their acting debut alongside each other in Rob Hardy's The Gospel (2005), which starred Boris Kodjoe and Idris Elba, and played Elba's daughters in Tyler Perry's Daddy's Little Girls (2007).

"This is the first time I've gotten to do some real acting with my sisters in years," Sierra noted, "and the fact that we're playing actual sisters is just the icing on an incredibly special cake."

9-1-1: Lone Star airs Tuesdays at 8/7c on FOX. Episodes are available to stream the next day on FOX Now or Hulu.