Queen Camilla is celebrating her 77th birthday, but her focus these days has been solely on the king.

King Charles III arrived at Parliament to preside over the State Opening, where he delivered his speech in his Robe of State and Imperial State Crown. He was accompanied by Camilla, who wore the George IV State Diadem.

Christopher Andersen, author of "The King," told Fox News Digital that Camilla has been dedicated to supporting her spouse, who is battling cancer. However, he claimed that the queen is worried about the monarch’s return to public duties as he continues treatment.

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King Charles III, wearing the Imperial State Crown and the Robe of State, sits alongside Queen Camilla, wearing the George IV State Diadem. He read the King's Speech from the Sovereign's Throne in the House of Lords chamber during the State Opening of Parliament at the Houses of Parliament on July 17, 2024, in London. (Henry Nicholls - WPA Pool/Getty Images)

"Camilla has been a rock for the king as he battles cancer," said Andersen.

"But she has grown weary of his behind-the-scenes complaining," he claimed. "She worries that he is not following doctors’ orders as closely as he should. She is concerned that Charles’ headstrong ways may be impeding his path to a full recovery. Any brief respite from the workload she has taken on is welcome, although despite Camilla’s trademark toothy grin, you can still see the strain. It’s etched on her face."

"While the king looks ruddy-faced and relatively robust, it’s really anybody’s guess how well he is doing medically," Andersen added.

King Charles III was diagnosed with cancer in February. (Wiktor Szymanowicz/Future Publishing via Getty Images)

Charles, 75, returned to public duties in April by visiting a cancer treatment charity. He and Camilla met with patients and staff at the University College Hospital Macmillan Cancer Centre in London during their visit.

The event was the king’s first formal public engagement since February, when Buckingham Palace announced that he would be taking a break from public duties to focus on his treatment for an undisclosed type of cancer.

The monarch has since been keeping busy with royal engagements. Camilla is often by his side.

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Queen Camilla has increased her workload in support of her husband, who is still battling cancer. (Hannah McKay - WPA Pool/Getty Images)

"Queen Camilla is a constant rock to her husband King Charles and is dedicated to her life of service," royal photographer Helena Chard told Fox News Digital.

"She works like a Trojan supporting the monarchy and is even working on her 77th birthday," said Chard. "She is radiant in white on her special day and is center stage as she joins King Charles at the State Opening of Parliament… I’m sure she never envisaged working on her 77th birthday and is looking forward to a much-needed quiet relaxing birthday cheer with her family, without the glare of camera flashes."

The palace previously said that doctors were "very encouraged" by the king’s progress, but his schedule would be adjusted as needed to protect his recovery.

Doctors are "very encouraged" by the king's recovery. (Justin Tallis/POOL/AFP via Getty Images)

While Camilla may still be adjusting to Charles’ carefully crafted comeback, royal experts told Fox News Digital there has been plenty of room for festivities to honor her special day.

"As customary for Camilla’s birthday, Prince William and Princess Catherine posted tributes and shared photos of Camilla, alongside birthday messages," royal expert Hilary Fordwich told Fox News Digital.

"The family, in past years, have gathered at Clarence House for a small family dinner," Fordwich explained. "Charles hosts an evening get-together for guests back at Highgrove. What she appreciates is for… the public to visit The Queen’s Reading Room, where she celebrates everything to do with books and the joy of reading."

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The Prince and Princess of Wales took to Instagram Stories to wish Queen Camilla a happy birthday. Kate Middleton is also battling cancer. (HENRY NICHOLLS / AFP / Getty Images)

Kate Middleton and Prince William wished Camilla a happy birthday by sharing a portrait of the queen on their Instagram Stories. The photo was taken by Kate for Camilla's "Country Life" cover in 2022.

Kate, 42, is also battling an undisclosed form of cancer.

"The birthday of an English queen is always a big deal, regardless of who wears the crown," Andersen explained. "In the morning, bells rang at Westminster Abbey. The band outside Buckingham Palace played ‘Happy Birthday’ during the Changing of the Guard. There were multiple cannon and gun salutes throughout the realm - in London, York, Edinburgh, and Cardiff. Camilla still had to show up for work… seated by her husband's side wearing full royal regalia as Charles presided over the opening of Parliament and delivered the 'King's Speech' outlining the new Labour Government's plans for the year."

The king traditionally delivers his speech from a golden throne while wearing the Robe of State and the diamond-encrusted Imperial State Crown. (Hannah McKay - WPA Pool/Getty Images)

"Once they were able to doff their ermine robes and gem-encrusted crowns - the king's Imperial State Crown is valued at upwards of $700 million - Charles and Camilla were able to relax, but not for long," Andersen continued. "They usually celebrate birthdays by hosting a relatively intimate dinner party for family and close friends at Clarence House. Ironically, Camilla is such a skilled social planner that she invariably winds up making all the arrangements for her own birthday parties.

Queen Camilla is celebrating her 77th birthday. (CHRIS JACKSON/POOL/AFP via Getty Images)

"Drawing up the menu and the guest list, deciding who sits where - Camilla revels in these tasks, which she once compared to ‘moving pieces on a chess board.’ As for gifts, the king has been known to dip into his late mother's spectacular jewelry collection to come up with some eye-popping pieces for Camilla: dazzling necklaces, earrings, bracelets, and pins - some of which once belonged to earlier queens like Queen Victoria, Queen Mary and the Queen Mother. The royals are reticent about flaunting their wealth, so usually these over-the-top birthday presents fly under the radar."

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"Often, no one is even aware of these gifts until Camilla is photographed wearing them at some event," Andersen added.

Camilla can look forward to the king slowing down on his grueling schedule. In a couple of weeks, the couple will head to Balmoral in the Scottish Highlands, where they will spend the rest of the summer unwinding with family.

King Charles and Queen Camilla will spend the rest of the summer at Balmoral. (Tim Graham Photo Library via Getty Images)

"They’ll spend the remainder of summer fishing, hunting, riding and hiking – as well as hosting a series of picnics, cocktail parties, dinners and even a full-dress ball," said Andersen.

Camilla was crowned queen in May 2023. Charles became king upon the death of his mother, Queen Elizabeth II. England’s longest-reigning monarch died in 2022 at age 96.

The Associated Press contributed to this report.