Prince Harry was savagely branded an “idiot” by John Lennon’s son Sean Ono Lennon. Ono Lennon, 48, sparked fury among the royal’s fans when he posted a joke about his book Spare, writing: “My long awaited review of Prince Harry’s autobiography is two words. ‘Spare Me.'” He doubled down on his criticism of Harry as he was slammed on social media. The musician also recalled meeting the late Princess Diana’s youngest son. Ono Lennon wrote: “Actually I am aware [that we have things in common]. We met once. That was before I realized he was an idiot.” Defending his initial post, the 48-year-old add…