Doctor Who Magazine Issue 879 (in-universe)

In a letter the Fourth Doctor sent to be printed in the first issue of Doctor Who Weekly, the Doctor recommended the 879th issue to his readers. (PROSE: A Letter from the Doctor)

Behind the scenes
When A Letter from the Doctor was released in 1979, the magazine was known as Doctor Who Weekly, however it later became known as Doctor Who Magazine. Another source recognised this change in name: in the narrative, the magazine was referred to as Doctor Who Magazine, as the name of the magazine by at least the 500th issue, so reasoning dictates that issue 879 to be titled under "Doctor Who Magazine".