Its B-side, "Pure Mystery", another spoken-word piece recited by Pertwee, had no connection to Doctor Who. It was used for the end credits of the Happy Birthday to Who (DVD: Revisitations 3) and More than 30 Years in the TARDIS video documentaries. John Levene sang this song once as a tribute to Jon Pertwee, but replaced the line "I'm the Doctor", with the words, "I knew the Doctor".