The British royal family isn’t unfamiliar with following certain rules and protocols, but there are a special few rules the Duchess of Cambridge Kate Middleton is expected to adhere to when she’s traveling.

Last October, after Kate had returned from maternity leave after welcoming her and husband Prince William’s third child, Express revealed that the royal “has to abide by some strict etiquette rules” when departing a plane.

“Female members of the Royal Family must keep their chin level to the stairs as they leave the plane,” the outlet wrote at the time, adding, “The etiquette rules mean the person not only has good posture but also allows the person to appear engaged with what is in front of them. While they hold their chin up they can also hold onto the rail as they descend to sturdy themselves.”

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Etiquette trainer Myka Meier explained the specific expected posture to The Sun, saying, “One should keep their back straight, chin parallel to the floor and square the shoulders.”

According to the outlet, Prince William is not required to follow the same rules as his wife. The publication noted that the Duke of Cambridge is usually seen exiting a plane ahead of Kate. This is reportedly done to ensure she doesn’t fall down the stairs and also to greet any foreign dignitaries on the tarmac.

Kate and William are not the only members of their family that have certain protocol to consider when flying. Express reported in a separate article last October that the couple’s children have begun to follow their parents and wave to their fans with their dominant hand.

“Kate is right-handed while William is left-handed, making it easy for them both to wave when close to each other,” the outlet explained. “Prince George and Princess Charlotte have both joined the couple on overseas visits... They too have perfected the royal wave which they show off when boarding the plane.”

Prince William, Prince George, Princess Charlotte and Kate Middleton
Prince William, Prince George, Kate Middleton and Princess Charlotte arrive at the Victoria Airport on Sept. 24, 2016 in Victoria, Canada. Getty Images/Chris Jackson