January 15, 2015 03:00 PM

Pippa Middleton is getting her sweat on post-holidays – with prominent Ashtanga yoga teacher Stewart Gilchrist.

Middleton was recently spotted at one of Gilchrist’s yoga classes in London’s trendy Chelsea neighborhood. There, PEOPLE has confirmed, Princess Kate‘s younger sister practiced the signature fast-flowing, intensive poses of Ashtanga in the hot-yoga style (classes take place in a heated studio to aid the release of toxins and loosen tight muscles).

It’s certainly not for the faint-hearted, but then Middleton, 31, is known for her hardcore approach to sports. Last year she completed a four-mile swim across the Bosphorus Strait from Europe to Asia, and – with brother James – she participated in Race Across America, cycling through 12 states in six days for charity.

As for Gilchrist, he told U.K.’s The Times that Middleton’s royal connections hold no interest for him. “I’m not really interested in that sort of stuff. I know who she is as of this morning. I treat everyone the same.”

The Scotland-born Gilchrist became a yoga teacher after suffering a severe back injury in his mid-20s. He has said that intensive Ashtanga Vinyasa yoga dramatically helped in his recovery.

Since then, he has worked with many leading yoga teachers and has a huge following in and around London, teaching 500 people at his classes every week. He’s also known for his celebrity clientele, having reportedly worked with stars like Kate Moss and Woody Harrelson.

As for Middleton will be back in the saddle, raising money for the British Heart Foundation, in June, when she takes on the London to Brighton Bike Ride, during which 25,000 cyclists descend onto the seaside resort each year.

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