Prince William's historic royal birth story as described by Princess Diana

Prince William hits a milestone birthday today. Forty years ago, on June 21, 1992, the Duke of Cambridge was welcomed into the world by parents Princess Diana and Prince Charles.

The late Princess of Wales was always a bit of a trailblazer, and was never afraid to tread her own path and it certainly wasn't any different when it came to the birth of her first son.

Princess Diana opted to give birth to her first baby at the Lindo Wing of St. Mary’s in London, which might not sound so unusual but previous to that, royal mothers had tended to deliver their babies in royal palaces.

While Princess Anne also gave birth to Peter Phillips, in 1977, and Zara Tindall, in 1981, in the same hospital, Prince William was the first heir to the British throne to be born in a maternity ward.

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Princess Diana had an idea of the type of birth she wanted too.

While royals previously gave birth in what has been described as a drug-induced "twilight" sleep brought on by a combination of morphine and scopolamine, while forceps were used to deliver their babies, Princess Diana, instead, wanted an active birth, during which she asked to remain fully conscious.

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Natural childbirth activist and author Sheila Kitzinger previously wrote in The Mail how she advised the Lindo Wing on the preparations for the birth of the prince.

"When she was pregnant with Prince William, I was asked to advise the private Lindo wing of St Mary's in Paddington, London, on what equipment it should provide so that she could give birth in an upright position," she wrote.

"I said that Charles looked strong enough to hold her. And that is what happened. It was the first active royal birth — a complete contrast to the Queen's reflection that, with modern anaesthesia, birth had become 'a sleep and a forgetting'."

Following a 16-hour labour, overseen by the Queen's own surgeon gynaecologist, George Pinker, who looked after the Princess throughout her pregnancy, Prince William was safely delivered at 21.03pm weighing 7lb 1oz (2.65 kg).

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While the finer details of royal births tend to remain private, Princess Diana revealed she had been induced with Prince William, due to media pressure surrounding the birth of her first child.

As reported in People, in Andrew Morton’s Diana: Her True Story she said: “When we had William, we had to find a date in the diary that suited Charles and his polo.

"William had to be induced because I couldn’t handle the press pressure any longer, it was becoming unbearable. It was as if everyone was monitoring every day for me.”

Princess Diana added: “Anyway, the boy arrived, great excitement. Thrilled, everyone absolutely high as a kite – we had found a date where Charles could get off his polo pony for me to give birth. That was very nice, felt grateful about that!”

Later, Prince Charles recalled his memories of the happy day in letter to his godmother, Patricia Brabourne, "I am so thankful I was beside Diana’s bedside the whole time because by the end of the day I really felt as though I’d shared deeply the process of birth and as a result was rewarded by seeing a small creature which belonged to us even though he seemed to belong to everyone else as well!" he wrote, as reported by Town & Country.

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The very fact that Prince Charles was present during the birth was also something of a royal departure and made him the first in a long line of royal dads-to-be to follow suit, including his own sons, who were at the birth of their own children.

Prince William was in the delivery room with the Duchess of Cambridge as she gave birth to Prince George, Princess Charlotte and Prince Louis.

Prince Harry was also keen to be by his wife, Meghan Markle's side, having been in the room at the Portland Hospital in Marylebone when Archie was born, and in the delivery room of the Santa Barbara Cottage Hospital for the birth of the couple's daughter, Lilibet.

After the birth, the Queen was the first royal relative to visit her grandson Prince William in hospital, going alone as Prince Philip was travelling at the time.

The way Princess Diana and Prince Charles introduced their tiny son, William, to the world also seemed to spark something of a royal trend.

The images of the couple posing happily on the hospital steps with their newborn, has since become something of a tradition that William himself continued with his own children.

While Princess Anne had also stopped for pictures after leaving the hospital with a newborn Zara, the first time a royal had done so, the images showing a first glimpse of the future king have remained iconic.

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But while they were all smiles on the steps, Princess Diana later spoke of a common struggle many parents suffer with.

In an interview for her biography in 1992, as per People, she described suffering from postnatal depression.

"Then I was unwell with postnatal depression, which no one ever discusses, postnatal depression, you have to read about it afterwards, and that in itself was a bit of a difficult time.

"You’d wake up in the morning feeling you didn’t want to get out of bed, you felt misunderstood, and just very, very low in yourself.

"People see it as crying wolf or attention-seeking, and they think because you’re in the media all the time you’ve got enough attention, inverted commas.

"But I was actually crying out because I wanted to get better in order to go forward and continue my duty and my role as wife, mother, Princess of Wales."