Proud Princess Eugenie has given royal fans a rare glimpse inside Buckingham Palace after sharing a candid snap of her father Prince Andrew on Instagram.

The royal, 28, shared the behind the scenes photo to celebrate her father's first Trooping The Colour as Colonel in Chief of the Grenadier Guards, an honour bestowed on him by the Queen in March, the Daily Mail reported.

"A wonderful and proud day celebrating Her Majesty's birthday and @hrhthedukeofyork for his first Trooping the Colour as Colonel in Chief of the Grenadier Guards," she wrote.

Saturday's Trooping The Colour saw the Duke ride out on the mall for the first time in full regalia and bearskins, alongside the Prince of Wales, the Duke of Cambridge and Princess Anne.

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Smiling Andrew, 58, looked smart in his regimental uniform as he posed in a corridor adorned with busts, paintings and huge free-standing urns.

An eagle-eyed royal fan commented that the painting seen over his shoulder showed the wedding of Princess Maud of Wales, a granddaughter of Queen Victoria.

The monarch commissioned Laurits Regner Tuxen to paint the scene which shows her granddaughter clasping her hand following her wedding to Prince Charles of Denmark in the Private Chapel at Buckingham Palace in July 1896.

Eugenie's snap delighted royal fans with many commenting on how handsome the Duke of York looked in his uniform, while others were pleased to see him looking so happy in the photo.

Saturday's Trooping The Colour saw him ride out on the mall for the first time in full regalia and bearskins, alongside the Prince of Wales, the Duke of Cambridge and Princess Anne.

Later, as he joined the rest of the royal family on the balcony for the fly past, Andrew played a subtle yet significant role by standing in for his father.

The Duke of Edinburgh, 97, who retired from public duties last year, was not by the Queen's side for the first time, but Andrew took his place by standing alongside the monarch - a spot usually occupied by his father.

His efforts on the day were also praised on social media by his ever-supportive ex-wife the Duchess of York.

Queen Elizabeth II and Prince Andrew during Trooping The Colour 2018. Photo / Getty Images
Queen Elizabeth II and Prince Andrew during Trooping The Colour 2018. Photo / Getty Images

Although she wasn't in attendance at the event, she posted several screenshots of TV coverage of the proceedings on Instagram, writing: "Very proud of @hrhthedukeofyork Colonel of the Grenadier Guards."

Most members of the royal family do not have their personal Instagram accounts open to the public, but the Duchess and her daughter Eugenie are exceptions.

Since opening her account on International Women's Day in March, the princess has delighted fans with her sense of humour and candid snaps.

Recently she shared previously unseen photos of herself holding court at a Buckingham Palace reception, joking in the caption: "In my next life looks like I could be a comedian."

Prince Charles, Prince of Wales, Prince William, Duke of Cambridge and Prince Andrew, Duke of York during Trooping The Colour 2018. Photo / Getty Images
Prince Charles, Prince of Wales, Prince William, Duke of Cambridge and Prince Andrew, Duke of York during Trooping The Colour 2018. Photo / Getty Images

Earlier this month she shared an unseen family snap with her sister Beatrice and parents the Duke and Duchess of York.

"90s flashback with Bea and parents to when my father commanded HMS Cottesmore," she said.

What is Prince Andrew's role with the Grenadier Guards?

King Charles II formed the Grenadier Guards at Flanders in 1656, making them his "Royal Regiment of Foot Guards".

The unit is now officially called The First or Grenadier Regiment of Foot Guards to honour their 1815 victory over the French Imperial Guard at the Battle of Waterloo.

Their iconic bearskin caps - which are worn for ceremonial duty - are also sported to recognise that victory.

Prince William, Duke of Cambridge with Prince Andrew, Duke of York and Princess Anne, Princess Royal during Trooping The Colour 2018. Photo / Getty Images
Prince William, Duke of Cambridge with Prince Andrew, Duke of York and Princess Anne, Princess Royal during Trooping The Colour 2018. Photo / Getty Images

Guards have won 78 Battle Honours, 14 Victoria Crosses and a George Cross after serving with distinction in campaigns including the Napoleonic, Crimean, Boer, First and Second World Wars.

As well as the soft power they bring to the world stage, Grenadier Guards were deployed for ground combat in Afghanistan.

Buckingham Palace announced in 2017 that Andrew would take over as Colonel in Chief from his father, who had held the role since 1975, as part of his renouncement of official duties.

His appointment was officially marked by a parade at Windsor Castle, Berkshire in March this year.

Andrew's new military title required him to appear on horseback at Trooping the Colour, prompting him to brush up on his horse riding.

Despite his family's love of horse's he's never been keen on the sport and was seen practicing on horseback in the run up to Trooping the Colour.