Prince Louis and Princess Charlotte have the “perfect mentor” as future royal spares to Prince George, royal fans have claimed. The word “spare” became a well-known metaphor for the younger sibling of an heir to the throne, after Prince Harry released his memoir last year. Many commentators have discussed how Prince William and Princess Kate will ensure Princess Charlotte, eight, and Prince Louis, six, do not end up with the same negative feelings. Their older brother Prince George, 10, is currently second-in-line to the throne, after his father the Prince of Wales. Fans took to social media t…