Prince Louis leaves royal fans shocked over rare 'grown-up' detail

Royal Family fans have been left shocked over one detail to do with Prince Louis that's shown how much he's grown.

For those who missed it, Kate Middleton's iconic annual Together at Christmas carol service took place on Friday (5 December) and as usual, was attended by a sea of famous faces who all showed up for the festive event.

Prince George, 12, Princess Charlotte, 10, and Prince Louis, seven, joined their mum and dad, Prince William at Westminster Abbey to take part in the evening of seasonal songs.

Among the celebrities at the high profile event were Kate Winslet, Chiwetel Ejiofor, Katie Melua, Eugene Levy, and Mary Berry to name just a few.

The 1,600 guests in attendance heard a mix of traditional carols, as well as music and poem and even a Bible reading from the Prince of Wales.

However, it was the royal children that stole the show, as fans couldn't help but comment on how much they were growing up - especially the youngest of the clan, Louis.

Royal Family fans couldn't get over how much Prince Louis has grown (Samir Hussein/WireImage/Getty Images)

Kate told told Dan Smith, lead singer with Bastille, that her children had been looking forward to the service: "They’re really excited, it’s become such a tradition."

The smartly dressed trio hung loops of red paper bearing their handwritten names on a 'Connection Tree', which represents togetherness and the importance of moments of connection.

As the night went on it got covered up with paper chains created as each guest left a loop with their name.

As we say though, people were most interested in Louis', Charlotte's and George's contributions - and notably couldn't get over the young prince's 'grown-up' handwriting.

His rarely-seen handwriting was spotted in a close-up picture of the tree, after he had penned his name on one of the paper chains.

The royal children were also later pictured holding candles with the rest of the churchgoers during the service and again, Royal Family fans were surprised by how much Louis has grown, as well as how much he looks like his brother George and mum Kate.

Taking to social media, one Twitter user wrote: "Prince Louis is identical in appearance to Princess Katherine(Kate)" while a second added: "Little Prince Louis isn't so little anymore!"

The youngster's 'grown-up' handwriting has drawn attention (Chris Jackson/Getty Images)

A third agreed: "Prince Louis has really changed gotten taller a proper little gentleman like big brother George."

While a fourth wrote: "Prince Louis is growing into such a mature & adorable young boy. His expressions are remarkably refined."

And a fifth added: "Prince Louis is growing up. This is such a sweet photo."

Another fan agreed: "Prince Louis absolutely rocking a double breasted jacket and did you see him fix his hair? He does that quite a lot - adorbs! As he grows up, I think he’s properly going to be into fashion - maybe even a Vogue spread?"

While someone else simply wrote: "Prince Louis looks grown up now."