How do they know? An anonymous "friend" of the expectant parents.
"A friend of the pair revealed: 'Some of Kate and William's closest pals were at a barbecue hosted by a family friend of the royals recently.They were all discussing the fact that Kate's baby is due to be born on July 13. Everyone was very excited.' "
Well, that sounds solid, doesn't it? And anyway, everyone knows that babies rarely cooperate when it comes to timing.
But if it is true, the baby will be greeted by a jubilant nation already in full celebration for the four-day Coronation Festival, July 11-14, to mark when Queen Elizabeth II, 87, was crowned in 1953.
She became queen on her father's death in February 1952, which was celebrated last year in a four-day Diamond Jubilee extravaganza. (Modern monarchs are typically crowned many months after they accede to the throne because it takes so long to organize a coronation, a religious and civic ceremony involving centuries of traditions.)
The Coronation Festival could rival the Jubilee party in hoopla, and a royal baby, a future monarch, would add to the exaltation.
But Prince William, 30, and the former Kate Middleton, 31, now the Duke and Duchess of Cambridge, will likely miss the festivities no matter whether the baby has arrived or not.
The palace has never specified the baby's due date; Kate herself mentioned to someone who asked that it would be around mid-July. The pregnancy itself was announced reluctantly late last year, but only because the duchess had to be hospitalized due to acute morning sickness.
Since then, her pregnancy — the first future monarch to be born since William's birth in 1982 — has been followed avidly by the public and the media, with rampant speculation about when it was conceived and the state of her baby bump.