Princess Mary wowed millions around the world when a stunning new portrait of the future Danish queen was released this week to mark her 51st birthday.

The Australian-born royal, who turned 51 on February 5, looked effortlessly chic in the photo wearing a recycled Carolina Herrera polka dot silk shirt dress, which she paired with minimal accessories, smoky eyes, a red lip and a ponytail.

Thousands who saw the snap were quick to say the Princess looks hardly any different to her wedding day in 2004 at age 32, which is in no small part thanks to a dedicated beauty and health regime that keeps the mother-of-four looking and feeling her best. 

FITNESS

One of the ways in which Princess Mary stays looking fit and young is through a targeted exercise regime that includes walking, jogging and horse riding.

'Mary, like the rest of her family, is totally dedicated to exercise. She's always walking, jogging, or riding a horse,' her sister-in-law Leanne Donaldson previously told New Idea.

This was in full evidence during the Princess's recent family trip Down Under for Christmas, when Mary was spotting both jogging around Sydney with her son and diving headfirst into the waves at Palm Beach.

Over the years, Princess Mary has been spotted trying her hand and succeeding in a number of sports, from tennis to charity fun runs.

She also reportedly has a personal trainer to help her stay in shape.

DIET

When it comes to her diet, reports suggest that the Australian-born royal has the 'Danish diet' to thank for her long, lean physique - a regime that is centred on locally sourced and readily available natural foods.

'People living in Denmark tend to eat more fish, especially oily fish like salmon and less meat than a typical Western diet,' Sydney-based dietitian Lyndi Cohen previously told FEMAIL.

'In the "Danish diet", the emphasis is on high quality meats when meats are eaten - and lean options.' 

A closer look at the regime shows the Danes typically have a lower intake of carbohydrates and a higher intake of good fats like nuts and seeds and protein.

'The Danish diet includes fruit and encourages snacking on berries, which are high in antioxidants that can protect against disease,' Lyndi said.

'It also includes plenty of root vegetables like carrots, parsnip and potatoes, while rye bread is a staple food in the diet - principally because it it much higher in nutrients like the B group vitamins, Iron, phytochemicals and magnesium.'

'Rye also contains considerably more fibre than white options, which can support a healthy and heart health,' she said.

The dietitian explained if Princess Mary is following the 'Danish diet', then she is likely to be snacking on plenty of fruit and vegetables and eating lots of oily fish, potatoes, nuts and seeds and cheese.

However, while Mary is disciplined, she is not overly so, as the Princess has been spotted regularly enjoying lavish dinners and glasses of red wine.

BEAUTY

The Danish royal has a dedicated approach to beauty, which is largely thanks to the Danish-born skin expert to the stars Ole Henriksen.

Ole Henriksen first met Princess Mary during her first pregnancy with son Prince Christian, when the Australian-born royal called on him for skincare advice. 

* Focus on the eyes as the most important aspect of your skincare routine - ensure the under eye area is hydrated at all times

* Drink plenty of water throughout the day, eat a diet rich in colourful vegetables and ditch junk food completely

* Invest in products containing high volumes of vitamin C to enhance your natural glow and boost radiance

* Exfoliate using products with natural botanicals every night to rejuvenate your complexion

* Maintain a regular exercise regime to stay physically fit and stimulate skin from the inside out

'Based on her love affair with a number of my products, she invited me to her residence. I found her to be incredibly warm, personable and extremely beautiful - I was mesmerised by her beautiful smile and stunning sense of style,' he told FEMAIL.

'We spent quite a long time together, and I just felt happy for my fellow Danes that someday, Princess Mary will be our Queen.'

The renowned cosmetician works with the Crown Princess on her skincare.

Mr Henriksen said the eyes are the most important area of the face and require 'special attention' as part of the wider skincare regimen. 

'Try to use creams proven to hydrate and firm to enhance your skin's elasticity, and always make this the last step of your routine,' he said.

'Nothing does it better than our Banana Bright Eye Creme ($54), which serves to illuminate and strengthen natural collagen with its added vitamin C - it's makeup and eye care in one jar!'

The beauty businessman stresses the link between a healthy, balanced diet and glowing skin, adding: 'I'm a strong opponent of fast food of any kind - say goodbye to junk and discover colourful vegetables instead.' 

Mr Henriksen emphasised the importance of drinking plenty of water, and said while you can still enjoy the occasional glass of wine, you must 'hydrate, hydrate, hydrate' in pursuit of your coveted complexion. 

He is an advocate of keeping physically fit at all times, and believes exercise 'empowers you to enjoy life to the fullest'. 

When it comes to makeup, the acclaimed Soren Hedegaard is Mary's personal makeup artist.

She is often responsible for creating her refined, regal look. 

Princess Mary typically favours a glowing base and pinky blusher, with a low-key smoky eye and either a nude or red lip. 

She frequently channels Danish up and coming designers when it comes to her fashion choices, as well as big name brands like Caroline Herrera and Marc Jacobs.