Dickie Arbiter, a former press secretary to Queen Elizabeth II, William's grandmother, actually sent a tweet -- "Kate's in through the front door." He quickly realized his mistake and sent a follow-up, "False alarm Sun stunt."
Tom Moore and Nicola Maher later posed outside the hospital revealing matching T-shirts under their now unbuttoned jackets: "The Sun No. 1 For Royal Baby News."
The baby, when it arrives, will be third in line for the throne after Prince Charles and Prince William. The child will keep that status because the rules of succession have been changed to become gender-neutral.
The royal couple have never released a specific due date beyond mid-July.