LONDON – It is probably the most famous engagement ring in the world. So it didn’t take long for a few people to notice that the Duchess of Cambridge’s ever-present sapphire and diamond sparkler had mysteriously vanished this weekend. Catherine, who was with her husband, Prince William, for the opening of a new cancer centre, was wearing the £250,000 Garrard ring, once owned by Princess Diana. It was a distinctive shock of colour against her oatmeal-coloured Amanda Wakeley dress. But one inside the hospital, the only jewellery remaining on her left hand was her plain gold wedding band. Of course, there was a simple explanation for the missing ring. Rather than misplacing it, or making some ill-timed statement about the state of her marriage, the Duchess had simply stowed it in her LK Bennett clutch bag for hygiene reasons on the advice of hospital staff. A palace source told People magazine: “The plan was always to take it off when she went into the ward in the same way the Duke and palace staff rolled up sleeves and tucked ties into their shirts.” They revealed that William’s jacket and Catherine’s clutch were left in the care of hospital staff while they were given a behind-the-scenes tour of the Oak Centre. They followed strict hospital protocol by rubbing antiseptic gel onto their hands. The Duchess also wore a small diamond-studded silver cross on a chain and diamond earrings by Kiki McDonough, which she was not required to remove.