Duchess Kate has a scar on her left temple. Often it is hidden and not visible, but every now and then it comes to light.

It's about eight centimetres long and has been a point of speculation in the past. Though scars are common, fans have still wondered how the Duchess got the mark. Was it from a serious injury or is it entirely harmless?

Duchess Kate's scar is from an operation

The line beneath the hair on her left temple was once theorized to be a sign of hair extensions. But this rumour was quickly eradicated by the Royal Family.

At the time, the Palace released this statement on the speculation: "The scar is related to a childhood operation." To this day, it's unclear why the Duchess underwent a procedure.

The Palace only commented briefly and said it was a private matter. However, in 2011, the Daily Mail even asked a surgeon who tried to get to the bottom of things.

He doubted that the scar was anything dangerous. Rather, it looks to him like a distant birthmark. But Kate isn't the only one left with scars from an injury.

Duchess Kate visits a primary school in London on Tuesday

Kate's husband Prince William also has a scar on his face. In March 2009, he inaugurated a new children's cancer centre at the Royal Marsden Hospital in London. One of the patients became aware of his injury and asked him what had happened.

William replied: "I was hit by a golf club while playing golf with a friend of mine. We pressed the green and before I knew it, an iron seven came out of nowhere and hit my head."

However, his scar is not always visible. It only appears in certain lighting conditions, which is why Prince William calls it his "Harry Potter" scar.

In an interview with CBBC a few years ago he revealed: "I call it that because sometimes it glows and then some people notice and sometimes they don't see it at all."