Matteusz Andrzejewski

Matteusz was a student at Coal Hill Academy in 2016. He was gay and as a result experienced conflict with his deeply religious Polish parents. He nevertheless accepted Charlie's invitation to join him as his date for the school prom.

He survived the Shadow Kin attack on the night of the prom, and was among the few students who met the Twelfth Doctor. (TV: For Tonight We Might Die)

According to Charlie, Matteusz was grounded when a dragon monster was attacking the school. (TV: The Coach with the Dragon Tattoo)

He was thrown out of the house by his parents for his relationship with Charlie. (TV: Nightvisiting) He subsequently lived with Charlie and Miss Quill. (TV: Nightvisiting, PROSE: What She Does Next Will Astound You)

Behind the scenes
The correct Polish spelling of the name is actually "Mateusz".

According to the official website, his name is Matteusz Andrzejewski. However, the full name has not been given onscreen.