Prince William and Prince Harry’s relationship was damaged years before Meghan Markle entered the picture, a royal author says. “People didn’t really acknowledge the fact that there was all this tension between Harry and William ever since they were small children, wrestling in the back of the car,” Christopher Andersen, author of “KATE! The Courage, Grace, and Power of the Woman Who Will Be Queen,” told Page Six in a recent exclusive interview. Andersen added that it was “made very clear” to Harry that “he was lesser than,” and that “left a real mark on them and really kind of doomed their relationship, ultimately.” Prince William and Prince Harry’s relationship was bound to be testy, says a royal author. Tim Graham Photo Library via Getty Images Royal author Christopher Andersen says there were issues long before Prince Harry met Meghan Markle. The California-based couple is seen here at the 2026 NBA All-Star Game.…