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EXCLUSIVE: Queen Elizabeth II was just 13 years old when the royal met the man that she would later marry.

The former princess met the then-18-year-old Prince Philip in 1939 when she joined her parents and younger sister, Princess Margaret, on a visit to Dartmouth naval college, People magazine reported. While Elizabeth was "reserved and shy" she was smitten by Philip’s "zest for adventure."

According to the outlet, the two exchanged countless letters while Philip served in the Royal Navy during World War II. After a year-long courtship, the couple married in 1947. The union lasted until Philip’s death on April 9th at age 99.

"The secret between their marriage was mutual respect, understanding and space," True Royalty TV co-founder Nick Bullen told Fox News. "As the duke, Philip knew that he had to do his duty. He was always there for the queen."

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Princess Elizabeth, later Queen Elizabeth II with her husband Phillip, Duke of Edinburgh, on their wedding day, 20th November 1947.

Princess Elizabeth, later Queen Elizabeth II with her husband Phillip, Duke of Edinburgh, on their wedding day, 20th November 1947. (Photo by © Hulton-Deutsch Collection/CORBIS/Corbis via Getty Images)

Bullen previously worked with the Duke of Edinburgh for a special commemorating his 90th birthday. He described how Philip stressed the importance of living a life dedicated to duty and service.

"He spoke of being this real guardian around the queen," said Bullen. "He protected her, but also made her passage through as a queen easier."

"I remember seeing it personally whenever he would walk into a room," Bullen recalled. "He just instantly broke the ice and put people at ease. So when the queen arrived, everyone was slightly calmer. People are terrified of the queen quite often because she is the reigning monarch. But he was a great icebreaker with a brilliant sense of humor. And he did it for the queen."

Philip gave up a promising naval career to become consort when Elizabeth became queen in 1952 at age 25. However, he was not content to stay on the sidelines and live a life of ease and wealth. Instead, he promoted British industry and science, espoused environmental preservation long before it became fashionable, and traveled widely and frequently in support of his many charities.

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Prince Philip, Duke of Edinburgh (R) and Queen Elizabeth II depart a Service of Commemoration for troops who were stationed in Afghanistan, March 13, 2015.

Prince Philip, Duke of Edinburgh (R) and Queen Elizabeth II depart a Service of Commemoration for troops who were stationed in Afghanistan, March 13, 2015. (Photo by Chris Jackson/Getty Images)

In his lifetime, Philip fulfilled more than 20,000 royal engagements to boost British interests at home and abroad. He headed hundreds of charities, founded programs that helped British schoolchildren participate in challenging outdoor adventures and played a prominent part in raising his four children, including his eldest son, Prince Charles, the heir to the throne.

When Philip turned 90 in 2011, the duke told the BBC that he was "winding down" his workload, adding he had "done my bit." It wouldn’t be until 2017 when Philip announced he was stepping back from royal duties and stopped scheduling new commitments. 

"The queen was very aware that when he retired, he wanted to go live in Sandringham in a small house on the estate," said Bullen. "And for a long time, in those early years of retirement, they didn’t see each other. But that’s what the duke needed. He needed that sort of space. They weren’t on top of each other. And it worked for them."

During his final months, Philip was isolating at Windsor Castle amid the coronavirus pandemic with Elizabeth.

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In this June 1, 2020 file photo, Britain's Queen Elizabeth II and Prince Philip pose for a photo in the quadrangle of Windsor Castle, in Windsor, England, ahead of his 99th birthday on Wednesday, June 10. Buckingham Palace officials say Prince Philip, the husband of Queen Elizabeth II, has died, it was announced on Friday, April 9, 2021. He was 99. Philip spent a month in hospital earlier this year before being released on March 16 to return to Windsor Castle. Philip, also known as the Duke of Edinburgh, married Elizabeth in 1947 and was the longest-serving consort in British history. 

In this June 1, 2020 file photo, Britain's Queen Elizabeth II and Prince Philip pose for a photo in the quadrangle of Windsor Castle, in Windsor, England, ahead of his 99th birthday on Wednesday, June 10. Buckingham Palace officials say Prince Philip, the husband of Queen Elizabeth II, has died, it was announced on Friday, April 9, 2021. He was 99. Philip spent a month in hospital earlier this year before being released on March 16 to return to Windsor Castle. Philip, also known as the Duke of Edinburgh, married Elizabeth in 1947 and was the longest-serving consort in British history.  (Steve Parsons/Pool via AP)

Bullen said there’s no denying that his passing is greatly felt within the palace.

"The queen said his death left a terrible void," he explained. "For her to have somebody she could really trust and rely on for the last 73 years – it must be devastating to lose such a partner. Not only was he a business partner because they ran ‘The Firm’ together, but also a life partner. I think like with any family, the senior royals are just trying to support the queen in these darkest of times for her."

Philip is survived by the queen and their four children — Prince Charles, Princess Anne, Prince Andrew and Prince Edward — as well as eight grandchildren and 10 great-grandchildren.

The Associated Press contributed to this report.