The 11-year-old is famous for his YouTube videos

Over the years, pint-sized rapper MattyB has built quite a following online.

At last count, his videos had a whopping 1 billion views.

Not bad for an 11-year-old.

But it’s his most recent endeavor – a YouTube video defending his younger sister, Sarah Grace, who has Down syndrome – that is really lighting up the Internet.

Sung to the tune of Cindy Lauper’s “True Colors,” he raps while 11-year-old Olivia Kay – another YouTube singing sensation – handles the vocals.

The video shows Sarah, who is the star, first being shunned by her peers, then being accepted. Though it was only posted Sept. 2, it already has nearly 4 million views.

“Sarah is just like any other normal kid,” MattyB (aka Matt Morris), who lives with his family outside Atlanta, told ABC’s Good Morning America Thursday.

The little girl, who has her own YouTube channel, agreed.

“I can do baseball or ballet, and I like to dance,” she told GMA. “I do hip-hop, and I play soccer, and I do batting, and I always play goalie.”

Their parents, who helped him write the song, couldn’t be more thrilled.

“It’s really so special to see Matt and Sarah interact,” Tawny Morris, their mom, said on the show.

MattyB hopes the video sends a message to other children with special needs.

“I hope they learn they can do anything,” he said.

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