Prince William Kate Middleton and Prince Louis
Pictured: Prince William and Middleton pose for photographers with their newborn baby boy Prince Louis of Cambridge outside the Lindo Wing of St Mary's Hospital on April 23, 2018 in London. Getty Images/Dan Kitwood

Prince Louis was once photographed sucking his thumb while at Prince William’s polo match. And it seems that this habit was something that another member of the royal family used to do.

When Prince Harry was still very young, he was oftentimes photographed with his thumb in his mouth. During his trip to Majorca with Princess Diana, the Duke of Sussex was photographed sucking his thumb while resting his head of his mom’s chest.

After Princess Diana saw what her youngest son was doing, she quickly removed Prince Harry’s finger from his mouth. However, Prince Harry sucked his thumb again.

In another photo, Prince Harry seems to be a little bit older but he is still sucking his thumb. He is sitting on the steps with Prince Charles and Prince William standing behind him.

Meanwhile, Prince Louis was also previously seen sucking his thumb at the Royal Ascot. While Middleton was carrying her youngest child, he popped his finger into his mouth. The Duchess of Cambridge also tried to remove Prince Louis’ finger.

While speaking with The Sun, restorative dentist Sally McCluskey of the Implant Center said that thumb sucking can be very damaging.

“Thumb sucking can be problematic as it can cause the alignment of the teeth to change, causing the upper front teeth to protrude and sometimes the lower front teeth to tilt backward. This can lead to problems particularly if the child falls over, as the teeth being in a more prominent position, can be damaged,” she said.

According to McCluskey, an increased overjet or the top teeth sticking out more than the lower teeth can also cause speech problems. But since thumb sucking provides comfort for many children, parents whose babies suck their thumbs shouldn’t feel bad.

She said that the formation of the teeth would still change as the child gets older and braces may also be used to make sure that the teeth are aligned.