A popular rap-meets-country song has inspired a Minnesota boy with autism to belt out some of his first words.

Until last week, 4-year-old Daniel Brundidge's vocabulary consisted of a few short phrases. But on Monday, the Cottage Grove boy suddenly started humming "Old Town Road" and then singing the words, shocking his mom and charming the internet.

"It was a breakthrough," Sheletta Brundidge said Sunday. "This is what I've been waiting on. This boy hasn't said more than three words at a time since he was born."

The change has been dramatic. Daniel sang the song, a favorite in his family, all week. His words have become clearer since he started singing and his eye contact is better. He's participating in activities with his siblings, which is also significant, she said.

"That lets us know he can learn at school, he can be taught in a certain way," Brundidge said. "We've just got to know what language he's speaking."

Ellie Wilson, executive director of the Autism Society of Minnesota, said that while everyone is different, combining words with music can be helpful to some people with autism because it provides a different way for the brain to process language.

"It's not unheard of that [with] kids who show delayed development of speech, the thing that really flips the switch can be music," she said. "Music can be an incredible tool."

Daniel's breakout came during a routine moment. Brundidge, a WCCO Radio producer and co-host of the "Two Haute Mamas" podcast, said Daniel, the youngest of her four children, was busy doing one of his favorite things after school Monday — buttoning and unbuttoning the housecoat she was wearing.

When he began singing the song, a country-rap mashup by Lil Nas X and Billy Ray Cyrus, Brundidge said she started crying. But she managed to record a 10-second clip of the boy on her phone. She stopped after that, she said, to be present.

"Somebody said, 'Why didn't you record more?' I said, 'Honey, I wasn't about to lose that experience looking through a phone. I want to be in that moment with my child,' " she said.

She called her husband in and the two tried to stay calm. When his siblings heard him, they knew it was a big deal.

"It was something about that song that touched his heart," she said. "It's not even like he was singing it, he was feeling it."

Brundidge tweeted Tuesday about her family's "#oldtownroad miracle." The tweet and the accompanying clip have since gone viral. Lil Nas X even responded by tweeting "What a King" and Cyrus retweeted the video.

The song isn't just a national hit — it's in heavy rotation at the Brundidge house, too. Brundidge said her family estimated they played it 47 times alone on Saturday. "Children love this song," she said. "It's like Lil Nas X and Billy Ray Cyrus ... live in my house."

Three of the four Brundidge kids have autism. The family moved to the Twin Cities from Texas in part so they could receive therapy at the Lovaas Institute in Minneapolis.

Brandon, 6, and Cameron, 5, have made great progress, she said, but Daniel had not — until now. His vocabulary previously consisted of tidbits like "bottle, please" or "lay down in bed."

His therapists have begun using the song to reinforce positive behavior with Daniel, letting him watch the video after he performs a task such as lining up blocks.

"Old Town Road" climbed the Billboard charts in April and gained national attention when Billboard removed it from the Hot Country Songs chart, declaring it not country enough. The song has now spent nine weeks at No. 1 on Billboard's Hot 100 chart and even broke the streaming record previously held by Drake, the Associated Press reported.

Lil Nas X, whose real name is Montero Lamar Hill, recently partnered with Wrangler and released a clothing line inspired by the song, according to the AP.

Brundidge said her children even want her to sing the song as a lullaby now.

"Everybody else's got 'Mary had a little lamb,' and the Brundidge babies is rocking the "Old Town Road,' " she said with a laugh.