Cher Monsieur le Président,

My wife and I were utterly heartbroken to learn of the terrible fire at Notre-Dame Cathedral this evening and wanted to let you know immediately how much we are thinking of yourself and the French people at this most agonizing of times, and of the emergency services who are so bravely tackling the blaze.  

I realize only too well what a truly special significance the Cathedral holds at the heart of your nation; but also for us all outside France it represents one of the greatest architectural achievements of Western Civilization.  It is a treasure for all mankind and, as such, to witness its destruction in this most dreadful conflagration is a shattering tragedy, the unbearable pain of which we all share.
  
Cher Monsieur le Président, our hearts go out to you and the people of France more than you can ever know, especially in view of our experience with the devastating fire at Windsor Castle twenty-seven years ago.  We send you our most profound sympathy, however inadequate that may be.  

Très cordialement à vous

Charles
The Prince of Wales