Although Kate Middleton has shared plenty of memorable moments with her other half, Prince William, over the years, she's also had some sweet and hilarious interactions with her brother-in-law, Prince Harry. He regularly has her laughing out loud when they attend events together, whether they're cracking up on the Buckingham Palace balcony or flashing big smiles in the stands. To make matters even cuter, Harry considers Kate "the big sister he never had." In an interview with Newsweek, the royal revealed that Kate, whom he refers to as "Cath," has helped him cope with the loss of his mother, Princess Diana. To get your royal-family fix, keep reading for a look at the duo's fun photos together, then check out the all-time best pictures of Prince William and Prince Harry.