Catherine, Duchess of Cambridge, has made a surprise appearance on the world’s longest-running children’s TV show.

Duchess Kate made a cameo on the British kids’ TV show Blue Peter to launch a new competition that encourages kids and their families to get more in touch with nature, Harpers Bazaar reports.

On the programme, Kate can be seen playing with a group of children and joining them in examining wildlife in a pond.

“We';re all ready to do a bit of pond-dipping,” host Lindsay Russell says, to which Kate responds, “Brilliant”.

When asked if she’s ever gone pond-dipping before, the duchess says the activity is “massively up my street”.

The mom of three also announced a new contest for people to design a sculpture for her Back to Nature Garden which she helped to design for the Royal Horticultural Society, E! Online reports.

The royal revealed that her family often spend time outdoors.

“Rain or shine, they get dragged outside,” she said.

“I see it encourages creativity, confidence. Even a short amount of time, 10 or 15 minutes, outside makes a huge difference, I think to both physical wellbeing and mental wellbeing.”

The episode, which aired in the UK yesterday, shows Kate taking part in a race to build a den and helping children create innovative plant pots, People reports.

For her participation, Kate was awarded the Blue Peter green badge for her efforts to get families back in nature.