Kate Middleton takes a hilarious stab at Prince William's running skills

From joking about her husband needing to use a toupee made from an alpaca's coat of hair to joking that she think he acts like a teenager, Kate Middleton has given us some hilarious one liner's about Prince William.

She has just hit him again with another zinger! The royal couple recently attended an event to highlight their mental health charity Heads Together Campaign. 

Good Morning Britain's
Sean Fletcher, revealed that Prince William had promised to run a marathon in Kenya sometime, to which Kate replied "I'll believe it when I see it."

This is probably her best one yet. We love their healthy competitive sides!