"It's moving all the time. I can feel it kicking now," she told 17-year-old Martina McDonagh during a visit to the Jack Tizard School on Monday, according to London's Telegraph.
The 33-year-old royal clutched her burgeoning belly as she spoke with the teen.
The local stop was part of Catherine's opening of the Kensington Leisure Centre in west London, which was built on the site of the 1970s pool where her husband and his brother, Prince Harry, learned how to swim. There, she was presented with a massive floating duck for 18-month-old Prince George, and she and her family were given a lifetime membership to the leisure center.
The duchess also opened the nearby Kensington Aldridge Academy. Earlier that day, the former Kate Middleton had a "coffee morning" with Family Friends in London, the palace said.
Prince George's mom is six months pregnant and is due in April. Her growing belly has started to show, although she concealed it Monday under a powder blue trench coat from Seraphine Maternity and a floral dress from the same brand.
Last week, the royals launched a new Twitter account, @KensingtonRoyal. Catherine, Prince William and Prince Harry had previously used Prince Charles and the Duchess of Cornwall's Clarence House account to keep royal watchers abreast of their whereabouts and their Royal Foundation.
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