Watch Prince William and Kate Middleton Get Cake-Making Tips From "Great British Baking Show" Finalist

In between their royal duties, the Prince and Princess of Wales have been working on their baking skills. The duo recently helped put the finishing touches on a birthday cake honoring the National Health Service's (NHS) 75th birthday, People reports.

The NHS refers to the United Kingdom's publicly funded healthcare services, which everyone in the country has access to. The celebration, held at St Thomas' Hospital in London, was hosted by NHS Charities Together—an organization of charitable organizations that support the NHS, its staff, volunteers, and patients.

As a way to celebrate the anniversary of the NHS, Prince William and Princess Catherine attended a tea party hosted in its honor. They were tasked with setting the tables, piping cupcakes, and detailing the birthday cake.

To help the royal pair with their baking duties, Alice Fevronia, a Great British Baking Show finalist, was there to show them the ropes. According to Fevronia, Princess Catherine was especially interested in learning how to hone her baking skills. "The princess was actually asking a lot of baking tips like 'How did you get the buttercream so smooth?'" Fevronia said. "She mentioned that she'd been up quite late on a couple of occasions trying to decorate the kids' birthday cakes."

It seems like those late-night baking adventures paid off for the Princess of Wales—her husband, on the other hand, could benefit from some practice. "The prince's piping skills were less good than the princess', shall we say," Fevronia said.

The cake the royals frosted was decorated in blue and white as a nod to the NHS. The main dessert also featured small doctors' clipboards illustrated with notable dates, like the day Prince William's late mom Princess Diana opened the first AIDS ward in the NHS, People reports.

Before presenting the cake to guests, Princess Catherine was tasked with putting on the topper, which read "Happy 75th Birthday NHS." Following their surprise arrival—cake in tow—Prince William and Princess Catherine sat down to chat with some of the event's guests. "They were just really fun," Fevronia said. "They were just having a fun time."