Kate Middleton's secret exercise to maintain her flat stomach and toned abs has been revealed.
The Duchess of Cambridge's size six figure is the envy of many royal watchers, with some questioning how she keeps in such trim shape.
Kate's love for the great outdoors is well-known, with the Duchess launching her own garden at the Chelsea Flower Show earlier this year to encourage others to get outside.
However, the royal relies on one particularly gruelling exercise to maintain her defined abdomen, according to the Daily Express .
The mum-of-three swears by an move called the plank, which is similar to a push-up except a person's forearms rest on the ground instead of their hands.
Plank practitioners have to maintain this position for a period of time, with the stance becoming more painful the longer it is held.
A source told Mail Online: "There are three elements, the basic plank, the side plank and the prone sky dive, all of which are positions Kate can hold for 45 seconds or longer and repeat at least ten times each.
"The side plank requires you to balance on your side, holding your body straight with feet together and one arm flexed directly under your shoulder.
"Meanwhile, the prone sky dive plank is slightly less excruciating, as you have to lie on your tummy and gently raise your chest off the floor until your tummy muscles beg for mercy."
She also uses an inflated gym ball to work her abs, an insider said.
Kate's impressive physique may also be down to active lifestyle.
The royal played hockey and tennis at school, as well as taking part in cross-country runs.
She is still a keen runner and apparently goes for a jog as often as possible around the family's Norfolk home, Anmer Hall.
