"Haley and Christina, if you guys are watching, thank you guys for being some of my best friends and supporting me all the way. I love you guys," he said.
The This Is Us star just turned 18 and didn't have a big celebration, he said, "I'm not a big celebration guy."
"I just went to the movies, but it's what I love to do, just studying other actors. It's the best birthday treat for me," he said.
When Blackk was nominated for his Emmy for When They See Us, he was 17 years old and the youngest nominee at the 2019 ceremony.
Catch him on This Is Us as Malik, a single father high school student romancing Randall's daughter Deja, on Tuesdays at 9 p.m. on NBC.
(E! and NBC are both part of the NBCUniversal family.)