"Eugenie had always been more than just a cousin to Harry," according to the book Finding Freedom
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Prince Harry and Princess Eugenie are royal cousins with a close bond.

News broke on Friday that Princess Eugenie and her husband, Jack Brooksbank, who are expecting their first child early next year, moved into Prince Harry and Meghan Markle's Frogmore Cottage home in Windsor.

"Frogmore Cottage continues to be the Duke and Duchess of Sussex’s residence in the U.K.," a source told PEOPLE, "and they are delighted to be able to open up their home to Princess Eugenie and Jack as they start their own family."

The move shows just how close Prince Harry and Princess Eugenie are.

"Eugenie had always been more than just a cousin to Harry. They were also the closest of friends," authors Omid Scobie and Carolyn Durand wrote in Finding Freedom: Harry and Meghan and the Making of a Modern Royal Family. "Out of all the Queen's grandchildren, Harry and Eugenie have one of the most natural connections. Like Harry, Eugenie is loyal, honest, and great fun. The two had many nights out together in London."

Prince Harry and Princess Eugenie
Prince Harry and Princess Eugenie
| Credit: Max Mumby/Indigo/Getty

"Harry had always confided in his cousin when it came to the women in his life," they added. "Not only did he trust her implicitly, but friends say that she gives great advice and has always been 'beyond wise' for her years."

Prince Harry and Princess Eugenie
Prince Harry and Princess Eugenie
| Credit: Pascal Le Segretain/Getty

And when Princess Eugenie and Jack announced that they were welcoming a baby in early 2021, a source told PEOPLE that Harry and Meghan — who relocated to California earlier this year after stepping down from their senior roles within the royal family — "sent their congratulations privately" to the parents-to-be.

Princess Eugenie & Jack Brooksbank with Prince Harry & Meghan Markle
Jack Brooksbank & Princess Eugenie; Meghan Markle & Prince Harry
| Credit: Getty Images (2)

However, there was a hiccup in the cousins' relationship when Meghan, 39, and Harry, 36, shared the news that they were pregnant (with 1-year-old son Archie) with family and friends at Eugenie and Jack's royal wedding in Oct. 2018. The pregnancy was officially announced three days later on the Kensington Palace social media accounts as the Duke and Duchess of Sussex embarked on their royal tour of Australia, New Zealand, Fiji and Tonga.

"It did not go down particularly well with Eugenie, who, a source said, told friends she felt the couple should have waited to share the news," according to Finding Freedom.

Princess Beatrice
Prince Harry, Princess Eugenie, Princess Beatrice and Prince William
| Credit: Julian Parker/UK Press via Getty

Eugenie, 30, and Jack, 34, previously resided in Kensington Palace's Ivy Cottage in London but have close ties to Windsor. The couple tied the knot at St. George's Chapel in Windsor Castle in October 2018, and Eugenie's parents — Prince Andrew and Sarah Ferguson — live just a few miles away at the Royal Lodge in Windsor Great Park. Eugenie's grandparents Queen Elizabeth and Prince Philip are also close by at Windsor Castle.

Frogmore Cottage
Frogmore Cottage
| Credit: GOR/Getty

In September, a spokesperson for the Duke and Duchess of Sussex said that Harry "fully covered" the renovation costs of Frogmore Cottage, which were said to be around $3 million. The costs had originally been paid by the Sovereign Grant, the U.K. fund set aside for royals that is fueled by taxpayers.

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The couple moved into Frogmore Cottage in April 2019 shortly before the birth of Archie. The original plan was to pay back the renovation costs in installments. The offer to settle their debts was made "proactively" by the couple, a source told PEOPLE, adding that the pair wanted to ensure that there was no ongoing drain on public monies as they strive to become financially independent.

"It is an important step that they have wanted to take,” said a source close to them. “It is something they have proactively wanted to do since the word go. They have taken the initiative to do so."