Princess Eugenie's wedding is tipped to feature a subtle yet touching tribute to Diana.

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Princess Eugenie was just seven years old when Princess Diana died in a car crash in Paris.

Twenty one years on, the royal is due to marry her partner Jack Brooksbank on Friday, in a ceremony that is expected to include a subtle nod to her late aunt.

According to royal commentator Richard Fitzwilliams, Princess Eugenie’s mother, Sarah, Duchess of York, will likely arrange a musical tribute during the nuptials at Windsor Chapel.

“She might choose a hymn which Diana was fond of such as I Vow To Thee, My Country, which was sung at Diana’s wedding and funeral,” he told Express.

Video by Mamamia

The Duchess, known to most as Fergie, was a close friend of Diana’s. Town & Country reports that the pair lunched together, even before Fergie began a relationship with Prince Andrew.

Once they became sisters-in-law in the mid ’80s, their bond strengthened. And again when their respective marriages began to breakdown.

In her autobiography, My Story, the Duchess wrote that, in 1991 – the year before they each separated from their husbands – “we first put words to the unspeakable idea that had been nudging us in the ribs for some time: that one or both of us might leave the Royal family.

“We burned the phone wires into the night, trading secrets and jokes that no-one else would understand.”

They fell out in 1996, around the time the Duchess’ autobiography was released. They didn’t reconcile prior to Diana’s death. She later told Harper’s Bazaar, “Because we were like siblings… we rowed. And the saddest thing, at the end, we hadn’t spoken for a year.”

Diana and Sarah in happier times. Image: Getty.

Though the Duchess was largely ostracised from the Royal family after her divorce (and the infamous toe-sucking incident of 1992), she is said to have forged a closer relationship with her nephews, Princes William and Harry, in recent years and was invited to the latter's May wedding to Meghan Markle.

According to Fitzwilliams, a gesture for their mother at Princess Eugenie's wedding would "undoubtedly please" the Princes.

“Sarah Ferguson has made a seismic effort to regain some of the royal favour she so catastrophically lost," he said.

“This wedding is her chance to excel.”

Well, if £2.8 million nuptials is all it takes...