Billie Piper (in-universe)

According to radio newscaster Rosemary Stark, "Billie" was a British singer and actress whose birthday fell on 22 September. (AUDIO: The Gathering)

There was a CD by the singer in Gwen and Rhys Williams' flat. (TV: Something Borrowed)

Behind the scenes
Billie Piper played companion Rose Tyler, and was in fact born on 22 September 1982.

In the invalid webcast Strax Saves the Day, Strax mentions whilst talking to the viewers of The Day of the Doctor that Billie Piper returned as "a completely different character".

Billie Piper's first album, (1998), was seen in Gwen Cooper and Rhys Williams' flat in the Torchwood episode Something Borrowed.