Elton John celebrated his 74th birthday last week with his "three wonderful boys" and shared a sweet snap of himself cutting into his birthday cake.But eagle-eyed fans have now spotted a rather hilarious detail in the birthday photo – Elton's apparent obsession with Marmite!MORE: Sir Elton John reveals the reality of homeschooling his two childrenTaking to Instagram on Thursday, he gave fans a sneak peek of his children's playroom as he posed with his cake – which was of numbers shaped into a