This decision was a “test of the Queen’s power”, the new ITV’s documentary titled The Real Crown: Inside the House of Windsor has claimed.
Appearing in the series, George Carey, who was the Archbishop of Canterbury at the time, said: “Charles and Camilla could not have an ongoing relationship that was open, you can’t do that.
“You can if you are an ordinary member of the public, you can’t if you are a member of the monarchy.”
During the party at the palace, Elizabeth II warmly celebrated her son, celebrating in a birthday toast his “diligence, compassion and leadership”.
Nevertheless, the late monarch appeared to share the same view as the now retired Archbishop, as demonstrated by her decision to exclude Camilla from the guest list.
The docu-series’ narrator said: “Before the party, the Queen tells Charles in no uncertain terms that she will never condone his relationship with Camilla.
“And so begins a power struggle between the Queen and the next in line.”
“Charles doesn’t want to go against the Queen’s wishes, but at 50 years old, not being allowed publicly to be with Camilla is becoming intolerable.”
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The then Prince of Wales eventually celebrated his milestone birthday, albeit privately, with Camilla, who reportedly hosted at Highgrove an event including some 250 guests. The late Queen and Prince Philip, however, were not in attendance.
A few weeks later, Charles seemingly moved against his mother’s wish to keep his relationship with Camilla a private matter, as he was photographed leaving The Ritz in London alongside his lover.
The documentary claimed the now King tipped off respected royal photographer Arthur Edwards in late January 1999, informing him there might be a photo opportunity outside the luxurious hotel in the capital.
After spending three days camped outside the venue, photographers were rewarded with the first-ever joint public appearance of the now King and Queen.
Together, the pair had attended the 50th birthday party of Camilla’s beloved sister, Annabel Elliot.
This move marked a turning point in the couple’s relationship and how it was viewed by the Firm and the public.
In June 2001, the pair took another key step on the road to public acceptance as Charles attended as Camilla’s guest a charity reception, where they exchanged a kiss on the cheek.
The Archbishop himself started having second thoughts on the future of their relationship and asked for a private meeting with the now Queen, during which he was “really struck” by her and by her deep love for the Prince of Wales.
Six years later, the late monarch agreed to their union and, after a short engagement, Charles and Camilla tied the knot in April 2005.
All episodes of The Real Crown: Inside the House of Windsor are available to stream on ITVX here.