There’s a great moment in the Beatles’ Get Back documentary — the 9 January 1969 session — when Mal Evans points out that the previous day had been Elvis’s birthday. Paul puts on his best Elvis voice and sings “God save our gracious King” … funny and appropriate too. Here are some relevant numbers:  

• Elvis had just turned 34 
• Paul was 26  
• Queen Elizabeth II had reigned for just short of 17 years 
• Paul had been 9 when Elizabeth came to the throne 

So Paul probably remembered (and perhaps still remembers) singing “God Save the King.” What goes around comes around.