It took years before Camilla was accepted behind palace doors – and the once vilified royal mistress was determined to earn the trust of Britain’s longest-reigning monarch.

Ingrid Seward, editor-in-chief of Majesty magazine, recently wrote a book, "My Mother and I." It explores King Charles III’s upbringing and relationship with his late mother, Queen Elizabeth II. Seward also sat down with the king, 75, at his Highgrove estate.

The royal expert told Fox News Digital that Camilla, who was crowned queen alongside Charles in 2023, wanted to prove her worth.

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A close-up of Camilla looking serious

It took years for Camilla to earn Queen Elizabeth II's trust. (Finnbarr Webster - WPA Pool/Getty Images)

"What Camilla did… she worked really hard at looking after Charles," said Seward. "Once she was married to Charles, she really took on the burden of royal duties, which isn’t easy for someone [who] hasn’t been brought up to it."

"Imagine going to a very grand wedding every single day and having to get up, dressed up, go out, meet people and talk to a lot of people you’re never going to meet again," Seward explained. "That is quite exhausting every single day. And this is for a woman [who]… was an army housewife. She was used to slopping around in her jeans, doing the gardening, going to her little shed and doing some painting, doing a bit of cooking, not really ever getting dressed up."

The book cover of Ingrid Sewards My Mother and I

Ingrid Seward has written a new book, "My Mother and I." (Simon & Schuster)

"But so suddenly to be thrust into that world was quite exhausting for her," Seward added.

Camilla walking outdoors in casual clothes

It took years for many in Britain to forgive Camilla, whose extramarital affair with Charles torpedoed his marriage to Diana, known as "the People’s Princess." (Barry Batchelor - PA Images/PA Images via Getty Images)

Charles met Camilla in 1970 through mutual friend Lucia Santa Cruz. According to reports, Charles was instantly smitten. Despite a blossoming romance, Charles joined the Navy in 1971. It’s also noted that Camilla didn’t meet the royal prerequisites for marrying an heir to the throne. The couple likely believed they didn’t have a future together.

While Charles was serving in the Navy, Camilla married Andrew Parker Bowles, an ex-boyfriend of Charles’ younger sister Princess Anne, in 1973. According to reports, a devastated Charles tried to stop Camilla from marrying Parker Bowles, but the pair remained friends.

Author Penny Juror previously alleged in her book, "The Duchess: The Untold Story," that Charles and Camilla began an affair around 1978 or 1979 and Parker Bowles was allegedly aware. As the pair stayed close, Charles began courting Lady Diana Spencer in 1980. Charles and Diana married in 1981.

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Princess Diana in a green outfit next to Prince Charles in a light blue sweater outside in Scotland

Princess Diana, the glamorous young mother of Princes William and Harry, died in a Paris car crash in 1997, five years after her messy, public split from Charles. (Getty Images)

Charles and Camilla reportedly began having another affair in 1986. In 1992, Charles and Diana announced their separation. During an ITV interview in 1994, Charles admitted to cheating on Diana. A year later, Camilla and her spouse called it quits, announcing in a statement they had lived apart for years.

Charles and Diana’s divorce was finalized in 1996. A year later, the Princess of Wales died in a car crash at age 36. While Charles and Camilla made their first public appearance in 1999, it wasn't until a year later that the queen acknowledged the relationship. 

Charles and Camilla married in 2005. The queen didn’t attend the civil ceremony.

Camilla smiling on her wedding day in between Prince Charles and Queen Elizabeth II

Queen Elizabeth II wasn't present for the civil ceremony of the former Prince Charles and Camilla. (ROTA-Pool/Getty Images)

Seward noted that, at first, the queen was "very wary" of Camilla’s efforts. But in time, she saw a different side of her daughter-in-law.

"Eventually, she realized how loyal Camilla was and how hard she worked at the job of being royal," said Seward.

But there was one act by Camilla that sealed the deal with the queen.

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Camilla wearing a powder blue coat standing next to Prince Philip in a beige trenchcoat

Camilla with Prince Philip, the Duke of Edinburgh. Queen Elizabeth II's husband died in 2021. He was 99. (Chris Jackson/Getty Images)

"She was wonderful with Prince Philip in his ailing years," said Seward about the queen’s husband of 73 years, the longest marriage for any British royal couple. 

"[Camilla] was really, really patient and very, very good with him," said Seward. "The queen… saw the warmth that Camilla had and realized that… Camilla was doing more for her son than she’d ever managed to do."

In February 2022, the queen said in a statement that Camilla’s title would be queen consort when Charles became king. 

Queen Elizabeth II smiling with her arms cross next to Camilla who is also smiling

Queen Elizabeth II and Camilla attend a horse show in 2015. (Max Mumby/Indigo/Getty Images)

"When, in the fullness of time, my son Charles becomes king, I know you will give him and his wife, Camilla, the same support that you have given me; and it is my sincere wish that, when that time comes, Camilla will be known as queen consort as she continues her own loyal service," said the queen when she marked the 70th anniversary of her rule.

Following the announcement, Charles said he and Camilla were "deeply conscious of the honor."

"As we have sought together to serve and support Her Majesty and the people of our communities, my darling wife has been my own steadfast support throughout," he said.

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Camilla in a sea green outfit and matching hat sitting in a carriage next to Queen Elizabeth II

Queen Elizabeth II and Camilla arrive in a horse carriage on day two of Royal Ascot at Ascot Racecourse on June 19, 2019, in Ascot, England. (Chris Jackson/Getty Images)

Seward said she wasn’t surprised by the queen’s announcement.

"[The queen and Camilla] were pretty close," she claimed. "I think the queen [had] a great sense of humor, and so does Camilla. She sees it as a glass half full, not a glass half empty. Charles sees it as a glass half empty. He always looks on the… negative side, or he used to… Camilla always looked on the positive."

"If she missed a train, she said, ‘Oh, don’t worry, there’s another one in 15 minutes,’" Seward continued. "But Charles would say, ‘Oh my God, it’s all going to be a disaster. I’m going to be late all round.’ So it was just a different way of looking at life."

Camilla riding a horse.

Camilla and Queen Elizabeth II bonded over their mutual love of horses and dogs. (Mathieu Polak/Sygma/ Sygma via Getty Images)

"I think the queen and Camilla looked at life the same way," Seward shared. "And also, they were both country women, and they loved horses and dogs, which always helps."

The queen, Britain's longest-reigning monarch, died in September 2022 at age 96. Days before the couple’s coronation in May 2023, Charles issued a royal warrant to change his wife’s title to queen. She is now known as Queen Camilla.

With the king and his daughter-in-law Kate Middleton currently sidelined by cancer, Camilla has helped pick up the slack. She has increased her schedule of appearances in her efforts to keep the royal family in the public eye.

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King Charles, Queen Camilla

King Charles III leaves the London Clinic with Queen Camilla after receiving treatment for an enlarged prostate. He was later diagnosed with cancer. (Mark Cuthbert/Getty Images)

The king has canceled his public engagements indefinitely after revealing that he is undergoing treatment for an undisclosed form of cancer.

Since becoming a member of the royal family, Camilla has taken on roles at more than 100 charities, championing issues that range from promoting literacy to supporting victims of domestic violence and helping the elderly.

Andrew Morton, Princess Diana’s biographer, previously told Fox News Digital that at one point, the queen and the future king were at odds over his true love.

King Charles III in limo

King Charles' relationship with his mother was tense at one point. (Victoria Jones/PA via AP)

"There was considerable animus between the houses of the queen and Prince Charles over Camilla," he explained. "[It was there] before [Princess] Diana died, and certainly after Diana died."

"The queen and her advisers, her courtiers, her private secretary – they all believed that Prince Charles should give up Camilla," he said. "He could love her, but he needed to leave her. And that’s because they felt she was damaging to the monarchy, which she was. There’s no question about that."

Morton alleged that the relationship between mother and son was so tense that a mediator had to step in.

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King Charles and Queen Camilla in royal regalia looking at each other while wearing crowns.

King Charles III and Queen Camilla on the balcony of Buckingham Palace following the coronation on May 6, 2023, in London. (Stefan Rousseau - WPA Pool/Getty Images)

"The presence of Camilla in Charles’ life did cause a rift between the queen and her eldest son, one which took several years to patch up," Morton explained. "And it wasn’t until the Archbishop of Canterbury, George Carey, intervened and said, ‘Look, I’ve spoken to Camilla on numerous occasions. She’s dedicated and loving. And her feelings for Charles are not going away.’"

"And what’s the queen’s job? It is to preserve the monarchy," Morton continued. "She sees this woman who is damaging the monarchy remaining in place. So it took a long time for that to be resolved."

The Associated Press contributed to this report.