Pippa Middleton Celebrated with a Gin and Tonic at the 47-Mile Finish Line of Her Big Race

"She got it just as she reached the finish line," Otillö founder Michael Lemmel tells PEOPLE

Photo: FameFlynet

Energy drinks? Yawn. After years of runs, swims, and bike races, super-athlete Pippa Middleton knows how to celebrate when she crosses the finish line.

And for her latest challenge, a grueling 47-mile swim-run in Sweden that she called “one of the hardest experiences I’ve ever had,” Princess Kate‘s younger sister toasted her victory with a gin and tonic (with lime!).

“She got it just as she reached the finish line,” Michael Lemmel, founder of Otillö, tells PEOPLE. “They all had the same, a tray full of gin and tonic with lime.”

Middleton competed alongside her teammate, Jöns Bartholdson, as well as her brother James Middleton and his teammate James Matthews. After meeting up during the race, the two teams crossed the finish line together, hand in hand.

The ultra-challenging course, which involves running over rough terrain and swimming through the choppy Baltic Sea, takes hours to complete – and 16 of the 115 participating teams failed to even do that.

“Anyone who finishes this race is in my mind a very, very good athlete, because it’s one hell of a course,” Lemmel says of the international event, which marked its 10th anniversary this year.

This year’s course was made even more difficult due to heavy winds and big waves in the Baltic Sea, where the swim portion of the race took place.

“Physically and mentally it’s quite a challenge to wrap your head around,” Lemmel says. “Going into the water into waves where you disappear on the other side.”

Even for the ultra-fit Pippa, the endurance event was a serious challenge – one that, at times, she wondered if she could complete.

“Throughout the race, we had doubts about carrying on and, ‘How are we going to finish?’ ” she said on Monday, the day after she turned 32. “But we made it.”

Pippa and her team of veteran athletes impressed Lemmel with their sportsmanship.

“She is amazing,” he said. “Not only did she finish the race, but she did it with great style but it was a very good performance. [I’m] very impressed, by her and all of them.”

For much more on Pippa’s ultra-athletic world, pick up this week’s issue of PEOPLE, on newsstands Friday