According to a royal insider, Princess Charlotte also “let the cat out of the bag” about a new royal baby with the 4-year-old telling everyone at school that her “mummy is having another girl”.
According to royal expert Aranzazu Santos López, there are two clues that the Duchess of Cambridge is about to make a pregnancy announcement.
"Look at these recent images of the return to school day. Look at Kate’s hair. It has a different air. Highlights or new colour, we don't know yet, but it's lighter, like a dark blonde," Santos López told Express.
"Every time the Duchess of Cambridge changes her look, she announces that she is pregnant within a few days."
For example, before announcing her pregnancy with Prince Louis, Kate debuted a new hair cut and when she was pregnant with Prince George, she cut a fringe.
Express suggested that Kate did this to distract from a growing baby bump.
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According to the royal commentator, the second clue that the royal couple are expecting their fourth baby is the fact that Kate's agenda has become locked.
"She will take time off, which could mean she is pregnant, considering that her previous pregnancies have been complicated," said Santos López.
In the past, the 37-year-old royal has been known to suffer from extreme cases of morning sickness (she was unable to attend Prince George's first day of school while she was pregnant with Prince Louis.
While Kensington Palace is yet to share any baby news, betting company Ladbrokes have shortened the odds on the Duchess of Cambridge giving birth by the end of 2020 to 1/2 this week.
Alex Apati of Ladbrokes told Express: “There'll be plenty for royalists to sink their teeth into next year if the latest odds are anything to go by, with a royal wedding and two babies potentially on the way.”