In the final moments of the “9-1-1” Season 9 finale, it was revealed that Buck has taken in preschooler Theo and will be fostering him after the unexpected car-crash death of Theo’s parents (who were Buck’s good friends).

For Stark, 34, the grounded finale made for the perfect bookend to a season that literally started with an out-of-this-world storyline.

Oliver Stark answers some rapid-fire questions about his co-stars for Decider.

During the final moments of the Thursday, May 7, episode, titled “Hearts and Flowers,” it was revealed that Buck signed paperwork making him the legal guardian of 4-year-old Theo after his parents, who utilized Buck as a sperm donor, both died in a tragic accident.

Photo shoot by Brian Zak for his interview with Decider.

Oliver Stark sits down with Sophia Soto to talk about the season 9 finale, his initial reaction to bringing Theo back, how Buck is going to approach parenting, how season 10 will further explore his decision, and more.

Oliver Stark breaks down the Season 9 finale for TV Insider.

We've added screenshots from Episode 18, "Hearts and Flowers," of Season 9 of 9-1-1.

We've added screenshots from Episode 17, "I Got You Babe," of Season 9 of 9-1-1.