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, along with April and Tanya's, to to kidnap Charlie and Miss Quill, using the alien body-swapping technology stolen by Garry Fletcher. The possessed Tanya threatened to kill Matteusz to coerce Charlie and Miss Quill into following them to the alien machine and fixing it. Matteusz was eventually returned to his body. (PROSE: Joyride)

In an effort to understand human Internet culture, Charlie posted pictures of Matteusz nearly nude. Matteusz was greatly upset by this, especially because he did not know Charlie has even taken the pictures, and did not forgive him until the next day. (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.