The Duchess of Cambridge's Scathing One-Liner About Prince William Running a Marathon Is Priceless

Who knew she was so funny?

From laughing about her husband needing a toupee made from alpaca hair to joking that she think he acts like a teenager, the Duchess of Cambridge has given us some hilarious zingers about the Duke of Cambridge.

However, this could be her best yet.

On Tuesday, the royal couple and Prince Harry attended an event to highlight their mental health charity Heads Together, where Good Morning Britain's Sean Fletcher revealed Kate had shared exactly what she thought of her husband's desire to run a marathon one day.

Fletcher told reporters: 'I chatted to Prince William, and he has promised that he will run a marathon in Kenya sometime.'

He added: "Then I spoke to Kate and she said, 'I'll believe it when I see it.'"

It's not entirely a surprise that Kate likes to joke about her husband's sporting prowess (despite him being an incredibly skilled polo player) as the pair have spoken about their healthy competitive sides on several occasions.

In 2014, the pair went out on yachts during their royal tour of Auckland, New Zealand where they separately competed in a race, according to E!.

Before the competition, Kate jokingly told William, "Take care!" before patting him on the back.

"Yeah, see you later," he replied, before his wife eventually took first place.

Kate, 1. William, 0.

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