Lithe and lovely Crown Princess Mary drew gasps of admiration as she stepped out to attend a friend’s wedding earlier this month. The poised princess, 39, has wasted no time in getting back into tip-top shape after giving birth to twins Vincent and Josephine in January. On the eve of her trip to Australia in November – her first official visit here since 2005 – Mary has again proven she is the queen of style. She’s certainly the perfect role model for post-baby fitness.

And, according to Mary’s Aussie family, there really is no secret to her slimline appearance. She’s just doing what comes naturally – leading a healthy, active lifestyle. “Mary doesn’t follow a strict diet at all,” reveals her sister-in-law Leanne Donaldson, who is married to Mary’s brother John. “She is so active she just burns the calories. Mary, like the rest of her family, is totally dedicated to exercise. She’s always walking, jogging, or riding a horse. And now she’s also running after four children – that’s guaranteed to keep anyone in shape!” Arriving at the Copenhagen wedding of family friends Sarah Kalbeitzer and Gregers Heering, Mary caused a sensation. She looked stunning in a purple silk dress that flattered her lean and elegant, 170cm-tall frame.

Her dramatic physical transformation has left the awestruck Danes wondering how a mum of four – who gave birth to twins only eight months ago – has suddenly developed the body of a supermodel. Leading Australian nutritionist Susie Burrell believes Mary is reaping the natural benefits of plenty of exercise and the healthy Scandinavian diet. “There are a lot of factors coming into play,” Susie tells Woman’s Day. “Having young, active kids and following a low-carb, high-protein diet are all linking together to give Crown Princess Mary that sensational, willowy, lean frame.

“The Scandinavian diet is a naturally high-protein eating plan. Mary would be eating a lot of foods high in omega-3 fats, a lot of good, oily fish, grains and nuts. The Scandinavians have far fewer obesity problems. Their diet is very low in processed carbohydrates – low in processed food in general. And Mary, following this diet, combined with her extensive exercise regime, is clearly being rewarded.” Sam Mower, an exercise physiologist and health consultant from Sydney’s Manly Beach Health Club, echoes Susie’s sentiments. “Mary is in peak shape because she has applied herself,” he says. “She has been eating the correct food and she’s obviously done what we call a strength program to enhance her resting metabolic rate. If you are weight training and you eat properly as you grow muscle, the muscle actually burns fat."

See Princess Mary's amazing new figure and read more about her health and fitness secrets in this week's Woman's Day on sale September 26, 2011.