He lost his child in a mass shooting. Now he’s telling his story in a solo show at NYC theater festival.

At the beginning of his one-man show, “Guac,” Manuel Oliver, a big, burly man with a bushy grey beard, takes the stage and turns to the audience.

“When you lose a son, what do you do?” he asks.

The question isn’t hypothetical for Oliver, whose son Joaquin, nicknamed “Guac,” was killed in the 2018 mass shooting at Marjory Stoneman Douglas High School in Parkland, Florida.

Oliver is performing in New York City’s United Solo Theater Festival from Friday through Sunday. The festival has been running for 16 years at Theatre Row in Midtown and will feature over 50 one-person shows, including “Guac.”

Despite the fact that he has performed his show in theaters across the country, Oliver does not consider himself an actor and had never performed until this show. He made a living as an artist and graphic designer for most of Joaquin’s life. Now, he’s a full-time activist.

“This is not in any way cathartic for me,” Oliver said in an interview from his home in Florida. “This is not in any way something that I do and then I feel better. I feel the same.”

But he said he still feels compelled to tell strangers his story and relive his pain over and over because he wants people to understand the personal consequences of gun violence.

“I’m not an actor, so it’s hard for me,” said Oliver. “I’m glad that somehow Joaquin is giving me that strength.”

“Guac” was presented in New York City in October at United Solo, where audiences named it best production.

The hourlong show recounts Oliver’s journey to Florida from Venezuela with his family, as well as his close relationship with his son.

But much of the show is silly and sweet despite its subject matter. For example, it details how Oliver and Joaquin bonded over their love of movies and rock and roll — particularly Lynyrd Skynyrd’s “Free Bird.”

“He knows how to connect with an audience in a way that most actors have a challenge doing,” said the show’s director…