King Albert II of Belgium's daughter faced criticism for her National Day outfit, which highlighted the work of a non-binary designer, with many fans calling it "inappropriate".

Princess Delphine is the product of an 18-year affair between her father, the former King of Belgium, and a Belgian aristocrat named Sybille de Selys Longchamps.

The 57-year-old attended the Brussels-based National Day in an ensemble created by Benjamin Voortmans, a young Belgian non-binary designer.

However, the red dress's daring thigh-high split received some negative reactions from royal fans, with one stating that the outfit was "inappropriate" for the patriotic occasion.

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National Day celebrates the separation of Belgium from the Netherlands in 1831, as well as the formal establishment of the Kingdom.

Revealing details of her outfit on Instagram, Princess Delphine wrote: "To celebrate Belgium on our National Day, I proudly wore a creation by @judassime (Benjamin Voortmans), a talented young Belgian designer and multidisciplinary, non-binary artist.

"We connect through a shared artistic language: transforming pain into beauty.

"I chose his work not only for his talent, but because it carries a message - one of tolerance, open-mindedness, and support for the LGBTQIA+ community.

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"I'm deeply affected by bullying and violence against those who don't fit the mould. This outfit stands for difference, freedom, and love. Viva la différence!"

Despite Delphine taking a stand as an ally to the LGBTQIA+ community, some found the dress inappropriate.

Taking to social media, one said: "Unfortunate and inappropriate, just to say the least." A second wrote: "Raunchy and inelegant."

A third added: "This is not an outfit a princess would wear for a national event." While a fourth said: "When I saw the photos, OMG....it was so inappropriate."

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For decades, the former King distanced himself from Princess Delphine and her mother to preserve his marriage.

In 2013, the year King Albert abdicated the throne due to health reasons and was succeeded by his son King Philippe, Princess Delphine launched a legal bid to be officially recognised as Albert's daughter, which she won in October 2020.

Now, Delphine has the right to bear the royal name de Saxe-Cobourg and is formally recognised as a member of the Belgian Royal Family, as are her two children, Princess Joséphine of Belgium and Prince Oscar of Belgium, whom she shares with partner James O'Hare.

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Delphine has started attending royal engagements, and her relationship with her father has healed after years of bitterness.

She met her brother, King Philippe of Belgium, in 2020, where they posted a socially distanced picture to Facebook, describing it as a "warm meeting".

When she was granted her royal title, Princess Delphine was also invited to Belvédère Castle in Brussels, where she had an official meeting with her father and his wife, Queen Paola.