The Danish princess donned the long cape gown with lacy sleeves while attending an event at Amalienborg Palace alongside husband Crown Prince Frederik this week.
And while she wowed onlookers with her outfit, many would not have noticed it was a gown recycled from a Royal visit to Japan in 2019.
Three years ago, the Australian-born royal wore the powder blue dress and decided to elevate the look for this week's affair as she further shows her commitment to wearing sustainable fashion.
She subtly altered the old dress to include the delicate lacy sleeves, and paired it with diamond earrings and Manolo Blahnik heels.
Princess Mary is known for recycling a number of designer gowns, including one by the late Australian designer Carla Zampatti.
In 2015 she was snapped in an official royal portrait wearing the design for the third time.
Princess Mary initially sported the dusty pink boat-neck dress in 2013 for a Women's Weekly photo shoot, then again to a state dinner the following year.
At the time, Zampatti told Fairfax Media at the time that she was 'so proud' that the Danish royal had not only asked to keep the dress but had chosen to re-wear it for such an auspicious moment.
"At the end of the shoot she asked if she could keep the dress [and] I was delighted.
"She looks so beautifully regal in their 2015 official portraits. I am so proud."
Some of Princess Mary's outfit choices date back 10 years, and she has been vocal about her dedication to sustainable fashion.
At the launch of the 2021 Copenhagen Fashion Summit, the Royal said we must take responsibility for what we buy and use and the impact of it on future generations.
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