Though the timing of the announcement of Charles' marriage plans is a shock, it's certain that it follows consultation with the Queen, the Archbishop of Canterbury, the prime minister and possibly constitutional experts too.
Mrs Parker Bowles will take the title of Princess Consort
The upshot is the kind of compromise which was denied to Charles' ancestor, Edward VIII.
In other words, Charles can become King and marry the woman he loves but she will never be Queen.
The significant difference between the two royals is that Edward was already King when his marriage to Mrs Simpson was mooted and it would have taken a change in the law to allow a so-called morganatic marriage to take place.
The government of the day, headed by Stanley Baldwin, set its face against that.
Despite the passage of 70 years since the abdication crisis, there are still constitutional implications to consider in Charles' marriage to Camilla.
As he is to become Supreme Governor of the Church of England, Charles could not marry a divorcee in a religious ceremony.
Hence the decision to choose a civil one in a setting - Windsor Castle - which carries no religious significance for the nation.
Critics will argue that this is hypocritical, but it is not incompatible with any existing law.
And as columnist Andrew Carey, son of the former Archbishop of Canterbury, has pointed out: "This is the path of least controversy.
"It would have been very difficult if Charles had ascended to the throne while maintaining an unmarried relationship with Camilla."
To the former shadow Attorney-General, Edward Garnier QC, it is evidence that "the British constitution is flexible and the arrangement which has been devised for this marriage is a highly pragmatic one."
The title to be adopted by Camilla after she has married Charles is chiefly a reflection of popular sentiment, which undoubtedly plays a far stronger role than it did in 1936.
The formal title, Princess of Wales, would have offended many people who blame Camilla for being the "third partner " in Charles' failed marriage to Diana.
However, Princess Consort has deliberate echoes of the title taken by Queen Victoria's husband, Albert, who worked diligently to win popular affection after suffering initial hostility.
The royal historian, Richard Waite, said the title Princess Consort is another way of saying that Camilla will be "Mrs King and this seems to chime with the sympathetic indifference which is how I would describe the popular view of the monarchy".