Princes William and Harry have resorted to writing their initials on the soles of their shoes after finding they kept picking up the wrong ones in their shared flat in London, a report said Sunday. The secret was revealed when someone spotted a "W" daubed on William's shoes at a charity gala he attended with his new wife Catherine this week, the Sunday Times reported. The newlyweds are sharing a flat in Clarence House with Harry until they move into their own place at Kensington Palace. "William and Harry are similar in shoe size, so I think this is his way of making sure he's wearing the right shoes. It's quite sweet, really," a royal source told the weekly newspaper. William and Catherine live in north Wales most of the time, where the prince works as a search and rescue helicopter pilot, but stay in London when they attend official engagements.