'Really wonderful': Prince William's special bond with his father-in-law Michael Middleton

One day in the not-so-distant future, Prince William will become King.

But while he has his father, King Charles, family members, friends and a palace filled with courtiers and aides, it is an unassuming man in his 70s whom William regularly goes to for advice: his father-in-law Michael Middleton.

While much has been written about William's bond with his mother-in-law Carole Middleton, royal expert Katie Nicholl has shed new light on his relationship with Michael Middleton.

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Nicholl, a British journalist and author who has been the royal correspondent for Vanity Fair since 2010, co-hosts the podcast Dynasty: The Royal Family's Most Challenging Year alongside Erin Vanderhoof.

During the most recent episode, Kate Middleton and the Future of the Monarchy, Nicholl described Michael Middleton, 75, as a "really wonderful father-in-law to William."

"I know they have a close relationship, [and] that William will often turn to Michael for advice," she said.

"I know he has a great sense of humour. I think he's someone who is a cool head in a crisis."

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Nicholl described Michael as "the quietest member of the Middleton family" — but that didn't stop him from making an hilarious speech at William and Catherine's 2011 wedding.

It marked one of the rare times he has ever spoken publicly about his son-in-law.

"I always remember his father-of-the-bride speech on the wedding day and how he had everyone at the tables just in fits of laughter when he was recounting the story of William, who was training at the time as a helicopter pilot, buzzing in on the Middleton family home and sweeping in on his helicopter," she said.

"Obviously, as a father, thinking, 'What on earth is going on here?' while simultaneously realising this was the future king of England really courting his daughter in a pretty spectacular way."

Nicholl added that the closeness of the Middletons at one time led to jokes among royal correspondents.

"We used to sort of joke about them being the 'en masse Middletons' when we used to write about them because they did everything together," she said.

"They would always stick together. They were a very tight unit [and] they're still the same today."

Nicholl's co-host Erin Vanderhoof added that the Middletons had given Prince William "a normalcy" that was previously lacking in his life.

She said reading Prince Harry's book Spare gave an insight into his and William's upbringing.

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"I think, as kind of a man as King Charles is, he was not necessarily the warmest, most open person," she said.

Nicholl said the Middletons surround themselves with a "very loyal circle of friends" who they trust not to divulge secrets about the Wales' family, which is why not much is known about what goes on behind closed doors.

However, she revealed Michael and the rest of the family had been on hand to help out during Catherine's recent health crisis.

"Certainly, in recent months, when Kate has really drawn on the support of her family and she's needed her sister to take the kids out, to help William, she's needed her mum there to cook and for Michael to take them off to the beach or whatever it might be that they're doing, and she has the most incredible support network in the Middleton family.

"They've been an anchor for her, more so now than ever before."

Nicholl said Kate's sister Pippa was also playing a big role behind the scenes.

"She's there, very quietly, but very much there for her sister," she said. "They are hugely close. Their children spend a lot of time together.

"I mean, it was no coincidence that Pippa was the one on the other side of Princess Charlotte in the Royal Box.

"Pippa is there more than most people realise."

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