Prince Harry struggled with growing up in Prince William’s shadow, but his role within the royal fold might’ve been defined at his birth. “Wonderful! Now you’ve given me an heir and a spare — my work is done,” Harry revealed King Charles told Princess Diana at the time of his birth in a Spare anecdote. According to a source, Harry’s position within the line of succession influenced his decision to write a memoir. “Harry’s resentment of being the ‘spare’ is the underlying theme of his book, through chapters on his childhood, his schooling, his career as a royal and in the British Army, his rela…