Donald Trump and Melania Trump broke major royal protocol when they greeted Queen Elizabeth, Prince Charles and Duchess Camilla at Buckingham Palace on Tuesday. Instead of curtsying and bowing to the members of the royal family, the U.S. President and First Lady shook hands with them, just as they did last June.

It is no secret that dealing with members of the royal family isn’t like dealing with anyone else —they’re bound by royal protocols, and it’s imperative that you know the basics if you’re meeting and greeting them in the flesh. But it looks like Donald and Melania aren’t giving a hoot.

Back in June, the U.S. President and First Lady made headlines when they ignored the curtsying tradition during a State visit. Donald Trump also walked ahead of Queen Elizabeth as they inspected the Honor Guards, forgetting that one of the major “don’ts” when meeting the Queen is turning your back on the monarch, as it’s considered incredibly rude.

Now, the Trumps are at it again. Arriving at the NATO reception at Buckingham Palace on Tuesday, Donald and Melania casually shook hands with the members of the royal family than doing the traditional bow or curtsy. While it is normal for some people to prefer to shake hands with the Queen when meeting her in person, the traditional form of greeting Her Majesty is bowing or curtsying.

Royal followers point out that as a State leader, Donald should have known better. Even Kate Middleton and Meghan Markle who are royals themselves curtsy to Queen Elizabeth when they meet her, so it’s understandable why many find it rude that the Trumps can’t even follow this simple tradition when greeting the Queen.

According to royal butler Grant Harrold, what made the Trumps’ handshakes worse was the fact that they were the ones who offered their hands to the members of the royal family. Melania did this on Tuesday when she was caught on video extending a hand towards Duchess Camilla upon meeting her. “You should never offer your hand to shake—wait for them to initiate the handshake,” Butler explained.