Adorable Prince Louis melts hearts as his eyes light up at the mention of a letter from Santa during Royal Carols: Together At Christmas: Social media goes wild for youngster as he joins parents Kate and William in a festive singalong

Prince Louis stole the nation's heart tonight as he joined a star-studded crowd to take part in the Princess of Wales' annual carol concert at Westminster Abbey.

Royal fans went wild when an adorable clip showed the young royal's eyes lighting up as actor Jim Broadbent, 74, read JRR Tolkien's The Father Christmas Letters.

The five-year-old, who reportedly had 'Christmas magic in his eyes', was seen nudging his mother Kate, whispering 'mama' and pointing at the award-winning actor as he read the note to the audience.

Upon entering the concert, the Prince and Princess of Wales' youngest child was seen posting letters to the North Pole, along with his older siblings, Princess Charlotte, 8, and Prince George, 10.

The trio were then seen alongside their proud parents – as well as other senior royals – holding candles and singing Christmas carols in the banquet hall filled with 1,500 people.

At the start of the show, which aired on ITV tonight, the young prince was seen posting letters to the North Pole with his siblings.

This year's Together At Christmas service – supported by the Royal Foundation – was held to honor those working to support babies, young children and families across the UK

This year's Together At Christmas service – supported by the Royal Foundation – was held to honor those working to support babies, young children and families across the UK.

While it was filmed on December 8, the full concert was broadcast to the public tonight on ITV.

Prince Louis was previously too young to attend his mother's annual Christmas concert, but his debut did not disappoint.

One wrote on social media: 'Look how excited Prince Louis was to see Jim Broadbent, it was beautiful.'

Another said: 'My favorite part of the whole service was Prince Louis' adorable reactions. He is so cute.'

A third added: 'He's a beautiful 5 year old with an enchanting smile for Christmas.'

Another adorable moment during the concert, caught on camera earlier this month, featured the youngster brutally blowing out his sister's candle during the concert, leaving his siblings in a tizzy.

The mischievous royal blew out Charlotte's candle as their mother Kate laughed. He was depicted puffing up his cheeks in an attempt to extinguish his older sister's candle as she smiled.

Prince Louis brutally blew out his sister's candle during Kate's Christmas carol concert, leaving his royal siblings in stitches

Prince George, Princess Charlotte and Prince Louis walk into Westminster Abbey with candles

Prince Louis was dressed in a checked shirt with a smart navy blue jacket and Chelsea boots

The Welsh children were on their best behavior as they greeted members of the clergy in the abbey's Lady Chapel.

Prince Louis looked shy as his older brother and sister smiled, shook hands and said hello to the priest.

Opening the ceremony, the Princess of Wales welcomed the audience who watched from home on Christmas Eve to revisit the service and spoke about the meaning of Christmas.

“Christmas is a time when we come together and celebrate the birth of a newborn baby,” she said.

'The arrival of each baby is a precious and memorable time, bringing us together to reflect on new beginnings and bringing hope for the future.

“During our earliest interactions, relationships and experiences, with those who love us, even before we are born, we lay the foundation for so much on which that future will depend. But only by valuing and supporting the vital role of adults in a child's world can we hope to make a difference.'

Prince William also took part in the service and gave a reading from the Gospel of Luke.

Among the group of celebrities who greeted the family were singers Beverley Knight, Adam Lambert and musician Jacob Collier.

Kate's sister Pippa and husband James Matthews were seen at the event, as were Lady Sarah Chatto and her husband Daniel Chatto.