Trump's tweet is referring to some invasive snapshots of Kate Middleton that were released a few years ago. If you recall, back in 2012, paparazzi snapped some topless photos of Middleton while she was vacationing on a private island. In fact, the six men accused of selling those photos (three photographers and three magazine publishers) just went on trial a few weeks ago and could face a year in jail in addition to a £38,000 fine. As for Trump, because of something called freedom of speech (long may it last), he got to make the comment on Twitter and pass it off as a joke. He faced some criticism back in 2012 and today, it came back around to the now-POTUS. Trump agreed to a visit to the U.K. later this year. While the queen, Prince William, and Prince Harry may be obligated by royal protocol to have some face time with the president, it'd be understandable if Middleton happened to be booked that day. After all, the royal hair doesn't wash itself.