Pippa Middleton may be a professional party planner, but on Monday, Sept. 16 the "Celebrate" author let someone else plan celebrity chef Jamie Oliver's Instagram party at Fifteen in London. The Duchess of Cambridge's 30-year-old sister enjoyed the party thoroughly and Revealed her hot body secret.

Pippa Middleton rocked the party in a French Connection blazer with a pink sweater and black mini-skirt for the bash. Pippa chatted with 38-year-old celebrity chef Oliver and noshed on an assortment of canapés. Other attendees at the party included musicians Boy George, Ashley Roberts, Ronnie Wood and ElizaDootlittle.

Oliver described the rendezvous as "fantastic" and "great" in an Instagram caption.

"Thank you to all the guys who we invited that came," he added. "It was such a pleasure to meet you all."

Pippa written her first "Sport and Social" column for the U.K.'s Telegraph three days earlier. In her column she explained how she came to be keen on boxing and transform her hot body.

"The air was heavy and sweet with the sweat of adrenalin-fuelled bodies. Every so often the dimly lit room seemed to shudder as a Tube rattled through far below," she wrote.

"I stood there a little uncertainly, well aware that in my slinky workout attire I was inappropriately dressed. The 20 or so men and women around me knew better, opting for loose-fitting T-shirts or wife-beater vests."

"This dingy location-a former air-raid shelter-under a railway arch was a club, but not the sort I was familiar with: no VIP areas here. As for Happy Hour...forget it. Skipping ropes, punch bags and an array of pungent-smelling gloves were the props," she continued.

"The Fitzroy Lodge Amateur Boxing Club in Lambeth, south London, is an altogether more serious establishment, the place where the famously intense actor, Daniel Day-Lewis, prepared for his role in the 1997 film The Boxer."

Pippa was at first nervous about boxing and asked a "fitness fanatic friend" for input. Hoping to get a "svelte silhouette," she agreed to try it.

"The basics of the boxing classes I attend at Fitzroy Lodge are the same week in, week out, rugged and ruthless: a five-minute skipping warm-up, not the school-playground-gallopy-type, but a boxer's skip, requiring speed and agility," she explained.

"The aim is to barely lift your feet off the ground, as if you're just tapping each foot over the rope, requiring balance and coordination."

After describing each aspect of the sport in detail, she added, "It's an hour and a half of pure but pleasing agony and by the end I'm broken, worn out and worn down, but I leave on a high, hiding the sweat patches under my hoodie, delighted to have found muscles and fitness I never knew existed."

Now we all know the secret of Pipa's "svelte silhouette," i.e. hot body.

Watch Pippa Middleton at Fitzroy Lodge Amateur Boxing Club in the video below:

www.youtube.com/user/Royalsdirect

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