Jealous Guy

In an unspecified parallel universe, Fitz Kreiner had encountered a song by the Beatles that had what Trix MacMillan said was the same tune as "Jealous Guy" with different lyrics. (PROSE: The Gallifrey Chronicles)

Behind the scenes
In the real world, "Jealous Guy" is a song released by John Lennon soon after the breakup of the Beatles. The implication of the reference is that in the parallel universe, the Beatles stayed together longer, and used the tune that Lennon created in 1970/71 for a different song.