What Kate Middleton accidentally revealed when she flashed her phone

Kate Middleton has accidentally revealed her favourite emojis are the swearing face and cucumber emojis in her latest "Early Years" video.

The Duchess, 38, flashed her iPhone 10 to the camera in her most recent video clip answering parents' questions about her campaign to help children in the early years of their development, writes the Daily Mail.

The video, shared to the Kensington Palace Instagram account, showed Kate thanking a "huge number" of followers who'd sent in questions with "wonderful emojis attached to them".

And the duchess's favourite emoji appeared to be two girls holding hands, usually representing friendship, with the pineapple emoji in second place - but the swearing face emoji would have caused the most surprise.

The vomiting emoji and the purple alien also featured, as well as the cucumber emoji, possibly presenting Kate's love of healthy eating.

And her seventh favourite emoji was the person bowing, while the last one was the wind cloud.

In the video, answering the question, "how do you manage temper tantrums in your household", Kate laughed and replied, "Yes, that's a hard one, I'd also like to ask the experts myself."

Kate also revealed that her interest in the early years of children's development is inspired by ambition for the "society we could and can become".

Kate's favourite emoji may have come as a surprise to her fans. Photo / Supplied

She's spent time looking into how early childhood experiences can cause challenges later in life such as addiction, poor mental health, family breakdown, homelessness and suicide.

"I think that people assume because I am a parent, that's why I have taken an interest in the early years," she said.

"I think this really is bigger than that. This isn't just about happy, healthy children. This is about the society we could and can become."

The duchess defined the early years as those from pregnancy to the age of 5.

"Right from the early days, meeting lots of people who are suffering with addiction or poor mental health, and hearing time and time again that their troubles now in adulthood stem right back from early childhood experience," she said.