Princess Kate refused to break this royal "rule" at the Chelsea Flower Show

There are many unspoken royal rules that seem fairly inexplicable to us mortals, but the latest one we've learned about actually does make quite a bit of sense.

During her recent visit to the Chelsea Flower Show, Princess Kate explained to some children that she's not allowed to use her signature, and while this may be a bit bizarre (and certainly disappointing for the kids), we have to admit it's not unreasonable.

At the event, the Princess of Wales joined pupils from Islington's St. Mary's Church of England Primary School and Brixton's Glenbrook Primary School to examine various bugs and beetles.

After being asked to sign some of the children's drawings, the royal said, "I can't write my name, but I can draw" (via People).

She added: "My name's Catherine. I'm not allowed to write my signature, it's just one of those rules."

Instead of signing the children's sketches, the princess drew a flower, a tree, and a pond.

Apparently, the reason royals aren't allowed to sign anything is because of the risk of forgery if their signature style were to become publicly known. Because royals have to sign off on all sorts of important documents, it could be quite dramatic if their signatures were forged.

This, unlike rules such as not being allowed to eat pasta (a rule it seems Princess Kate has in fact managed to shirk) feels perfectly justified.

Kate made a surprise appearance at the annual Chelsea Flower Show on Monday. For the occasion, she rewore a two-toned bright pink dress by ME+EM, and participated in a Children's Picnic with schoolchildren, as well as meeting the Chelsea Pensioners group.

On the day, she made a couple of other sweet and surprising revelations.

Firstly, she revealed one of Prince Louis' school-day activities. "Louis is growing broad beans at school," she said.

And secondly, she shared the secret to being a successful member of the Royal Family. "You have to work hard," she told a little girl who had asked.

The royals are understandably private, so it's always nice when we learn some new details about their lives!