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) On his first night staying there he admitted to Charlie that he loved him and the pair ended up having sex. After Charlie saw his parents due to the Lan Kin's influence, he helped Charlie and Miss Quill defeat the creature, discovering on the way to Tanya Adeola's flat that every time he severed part of the creatures roots they immediately reattached. (TV: Nightvisiting)

Matteusz's body was taken over by Steve Hopley, as were April and Tanya's, in an effort to kidnap Charlie and Miss Quill for their assistance with the alien technology stolen and repurposed by Garry Fletcher. The body-swapped Tanya threatened to kill Matteusz if Charlie and Miss Quill would not aid them. Matteusz was eventually freed by a body-swapped Ram, pretending to Garry Fletcher. (PROSE: Joyride)

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.