Marriage is a tough business, and every couple is different and uses different techniques and strategies to make it work. Prince Charles and Queen Camilla's relationship has been controversial at times, but has truly stood the test of time.

The Daily Express has reported on the secret to their successful marriage. Charles and Camilla have decided not to live at Buckingham Palace, the official residence of the monarch, for now anyway. (They also don't live at Windsor Castle, where Her late Majesty spent time.) She has lived at Clarence House for many years. He also has several other properties where he can escape when he needs to get away from his work or when he and I argue lovingly with each other. Clarence House has three bedrooms: one for the King, one for the Queen, and one that they share.

Interestingly, married members of the Royal Family traditionally have separate bedrooms. Queen Elizabeth and Prince Philip did so (not only in separate bedrooms, but in completely separate wings), as did the Prince and Princess of Wales when they lived at Kensington Palace. Prince Charles' need for his own bed is not sinister, but actually stems from his health. The King suffers from chronic back pain, and sleeping alone is said to relieve the pain.

Royal expert Joshua Lom added that the couple prefer separate bedrooms because of their busy schedules and prefer to relax separately; the two sleep separately not only at Clarence House, but also at Highgrove, their country home. Camilla is said to have her own room there, but does not spend much time there, preferring instead Ray Mill, where her family is close by.

Sleeping separately is said to be the secret to the King and Queen's long-lasting marriage, friends say, because it allows them to have their own designated space and a shared space for when they want to use it.

"His Highness has a room with a double bed, decorated to his taste, and Camilla has her own room with a double bed, decorated to her taste. In addition to that, there is a shared bedroom with a double bed, which you can use whenever you like. This arrangement is perfect for the two of us."