Prince George, Princess Charlotte and Prince Louis soaked up the magic of Christmas as they joined their mother for her annual televised carol service.

The three royal youngsters stole hearts as they arrived and immediately – with expressions of adorable seriousness- made a beeline for a bright red letterbox that had been placed outside Westminster Abbey.

It had been put there at Kate’s request so that members of the congregation could post handmade Christmas cards and letters to children less fortunate than themselves.

The Christmas cards will be distributed by charities, including Child Bereavement UK, East Anglia Children’s Hospice, Evelina London and the British Red Cross, as a surprise gift to children. The Princess of Wales encouraged guests to bring a card for children who might struggling this year.

Prince George’s letter was addressed to Tony, potentially Tony Hudgell, the nine-year-old boy who has raised millions of pounds walking vast distances on prosthetics after his legs were amputated in infancy due to horrific abuse.

Princess Charlotte of Wales, Prince Louis of Wales and Prince George of Wales post Christmas letters before The ‘Together At Christmas’ Carol Service at Westminster Abbey

Tony, from West Malling in Kent, met royal mother-of-three Kate, 41, at Evelina London Children’s Hospital earlier this week, where he and his mother Paula chatted with her – and Paula was pictured feeling a little emotional at the meeting.

While George, ten, looked smart in a suit, little Louis, five, wore a navy buttoned up jacket. Charlotte was equally stylish in a burgundy coat – and immediately made a beeline for her mummy’s hand. Louis grabbed onto his father, Prince William.

The three youngsters had arrived in a car with their father as their mother, elegant in all white including a Chris Kerr coat, had travelled to the Abbey an hour earlier to check on arrangements and meet performers and members of the congregation.

Inside the Lady Chapel she met the performers and confessed to admiring American singer Adam Lambert. She also told how Princess Charlotte was learning the piano and had watched singer songwriter Jacob Collier playing on YouTube.

She told Lambert, who was the first singer on stage at the Queen’s Platinum Jubilee last year when he sang We Will Rock You with Brian May: ‘I was a big fan of your performance at the jubilee. Thanks for being here.’

The Princess told Jacob Collier, who performed George Michael’s Last Christmas on John Lennon’s old piano at the service, that she and Charlotte had been watching him play piano on YouTube.

‘I said to Charlotte it takes a lot of practice. We saw you on YouTube,’ she told the musician, who confirmed afterwards that the future Queen had told him Charlotte was learning to play piano.

He told Kate, an accomplished amateur pianist, it involved ‘a lot of plinking and plonking’.

Prince Louis sweetly greeted The Dean of Westminster, David Hoyle, with a firm handshake upon his arrival

Kate asked singer Freya Ridings if she had ever been into the Abbey before. ‘No, I was born here and I’ve never been before,’ Ridings said, waxing lyrically about the beauty and splendour of the Gothic masterpiece.

Singer Beverley Knight told Kate that the high ceilings in the Abbey made for perfect acoustics.

The Princess thanked each of the performers for giving their time.

‘Thank you, thank you so much,’ she said. Singer James Bay told her: ‘It’s a pleasure. I’m happy to be here.’

Also present were Kate’s parents, Michael and Carole Middleton, sister Pippa, Zara and Mile Tindall, the Duchess of Edinburgh and Princesss Beatrice and Eugenie.

Prince George, 10, Princess Charlotte, eight and Prince Louis, five, put on an adorable display in matching outfits for the event.

Prince George appeared to post a Christmas letter to a ‘Tony’ before entering the Westminster Abbey

The children put on a sweet display – and matched their outfits to a colour theme of crimson and navy

King Charles’ eldest grandson and the second in line to the throne matched his father for the occasion, and looked dapper in a navy suit with a crimson red tie.

His younger sister Princess Charlotte personified the elegance of her famous mother as she donned an elegant crimson red coat.

Meanwhile Prince Louis looked just as stylish as his eldest brother in a navy ensemble, cord trousers, and Chelsea boots.

Evidently honing their fashion prowess from their father, the future king matched his children and donned the on-theme colours of crimson and navy.

The royal family were among many who stepped out to witness the princess perform at the special Christmas service, which is poised to honour those who work to support babies, young children and families in communities across the UK.

It comes as Kate also stepped out tonight to attend the glittering Christmas event at Westminster Abbey in London.

Charlotte held on to her mother’s hand as they entered the carol concert this evening

Prince Louis looked dapper in a navy ensemble- complete with a matching pair of suede Chelsea boots

George, Charlotte, and Louis each held a candle at the service, with Edo Mapelli Mozzi following shortly behind

The children put on a sweet display as the participated in the evening’s events

Princess Charlotte gave a sweet smile as carried a candle in Westminster Abbey next to her younger brother Louis

The Prince and Princess of Wales and their children arrived in style to the Christmas carol service at Westminster Abbey

The Princess of Wales, 41, who is hosting the Together At Christmas service, looked festive in a cream ensemble.

The mother-of-three was joined by the Prince of Wales and their children Prince George, 10, and Princess Charlotte, eight, and Prince Louis, five.

The service – attended by the King Charles and Queen Camilla – will recognise the selfless efforts of communities throughout the UK, highlighting the importance of coming together to support one another.

Spearheaded by the Princess, it will combine both traditional and modern elements, reaching people of all faiths and none.

The service, Royal Carols: Together at Christmas, will then be shown on ITV on Christmas Eve.

The service will see the world-renowned Westminster Abbey choir perform some of the nation’s most beloved carols, alongside musical performances by guests including Jacob Collier, Freya Ridings and James Bay, and a special duet from Beverley Knight and Adam Lambert.

Poignant readings will be delivered by speakers including Prince William, Micheal Ward, Emma Willis, Roman Kemp, and Jim Broadbent.

A specially commissioned poem written by Joseph Coelho, the Children’s Laureate, will also be read by Leonie Elliott.

Prince Louis held onto his father’s hand as they walked into the carol concert alongside Kate, Charlotte, George, and Reverend Dr David Hoyle

Prince George, Princess Charlotte and Prince Louis all arrived clutching letters to send off before the service

The royals put on an elegant display- and William matched his children’s outfit with a colour theme of navy and red

Princess Charlotte and Prince George accompanied their mother at the service, which is supported by The Royal Foundation

Kate, who arrived at the service earlier in the day, greeted her family as the arrive together in a blue car

The broadcast will also feature an introduction from Kate and films which bring to life the importance of early childhood and celebrate the remarkable contribution people in our communities are making to support the very youngest members of our society during those crucial early years.

These will include contributions from Rio and Kate Ferdinand, Ugo Monye, Andrea & Virginia Bocelli and Dame Sheila Hancock.

The service will see Westminster Abbey filled with sustainable, eco-friendly festive decorations, providing a beautiful Christmas backdrop, nodding to the theme of children and families.

New features this year include a Christmas Post Box located outside the Abbey for children to send handmade Christmas cards and best wishes to other children who might be struggling this year.

In addition, guests will be treated to carols and Christmas songs upon arrival from the Action for Children Young Carers Aloud choir, made up of 12 young carers, the youngest of which is just six years old.

Guests attending the service have been nominated by Lord-Lieutenants across the nation, in addition to charities associated with Members of the Royal Family.

They will be joined by those working in the early years space which is a key focus area of The Princess of Wales’s work through The Royal Foundation Centre for Early Childhood.

It will also consist of those who may have had a challenging year, including children and families, or those who might find the winter period difficult.