Find out what unusual sleeping arrangement King Charles III and Queen Camilla have and which other royals do the same.

King Charles III and Queen Camilla’s (formerly known as Camilla Parker Bowles) marriage is the second for both of them. But they have been married to each other longer than they were to their first spouses leaving some to wonder what the secret is to their marriage. Well, that just might be linked to their unusual bedroom arrangement.

King Charles and Queen Camilla do not sleep together in the same bed or in the same room for that matter. “[Charles] has a room with a double bed, decorated to his own taste, then Camilla has her own room with a double bed, decorated just the way she likes it,” a friend of the king and queen told the Daily Mail.

While that seems like an odd arrangement for some, it’s not uncommon with royal couples. “In England, the upper class always have had separate bedrooms. You don’t want to be bothered with snoring or someone flinging a leg around,” explained Queen Elizabeth II’s cousin Lady Pamela Hicks. As The Mirror noted, another reason for the arrangement may have to do with the king’s health as the monarch has suffered from back pain for years and sleeping alone in a bed makes things easier for him during the night.

Moreover, royal expert Joshua Rom suggested that separate bedrooms may also have to do with the fact that the king and queen have such hectic schedules and are around so many people all the time that they prefer to relax separately. Some reports even claim that the arrangement is the “secret” to the pair’s “long-lasting marriage.”

But they aren’t the only royals to have adopted such a sleeping arrangement. It’s been reported that Prince William and the Princess of Wales (formerly known as Kate Middleton) do not sleep in the same bed at their Kensington Palace residence. Some believe that because William’s wife suffers from hay fever and sleeping in her own bed soothes her allergies.

Queen Elizabeth and Prince Philip did not sleep in the same bed either. As depicted in The Crown, their Buckingham Palace residence had two large sleeping quarters separated by a central room with double doors and when those doors were open, the couple could see each other across the divide. The late queen and her husband were married for 70 years. So perhaps that is the secret to a long marriage which is good news for the other royal couples who sleep separately.