Prince Louis appeared muted while his siblings, Prince George and Princess Charlotte, joined in with the Christmas Carol Service.
The seven-year-old was seen looking around as he stood next to his mother, Princess Kate and sister, Charlotte.
George and Charlotte both sang hymns from their book during the ceremony at Westminster Abbey.
Louis, who had a book at the start of the service, eventually stood with his hand in his pocket as he held his candle like the rest of the auditorium.
Prince Louis appeared muted during the service | GETTYTRENDING
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At the beginning of the broadcast, Louis's sister Charlotte performed a duet piece alongside her mother, Kate.
The performance was accompanied by a voiceover from the Princess of Wales reading the letter handed to guests at Westminster Abbey.
The pair played Holm Sound by Scottish composer, producer and multi-instrumentalist, Erland Cooper.
Charlotte and Kate often play the peaceful tune together at home.
Louis started the ceremony with his service book, but was later without it
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The special moment was recorded in the Inner Hall at Windsor Castle.
The broadcast went out on ITV1 and ITVX with a repeat airing on Christmas Day morning.
BBC Studios Events and The Royal Foundation co-produced the programme, which included two special films showcasing individuals and organisations who have demonstrated love and compassion to others during difficult times.
Kate has played the piano at previous festive concerts in the past, including in 2021, when she put on a heartfelt performance at a Westminster Abbey service which aired on TV.
The Waleses sat in the front row, alongside Zara and Mike Tindall and the Duchess of Edinburgh
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Louis's father, the Prince of Wales, delivered a Bible reading during the ceremony.
William read from the Gospel of Luke, 2:8-16, as Kate smiled towards her husband.
The future king delivered his speech confidently, taking moments to pause while speaking at a moderate pace.
The Waleses were joined by a series of other royals, including Zara and Mike Tindall and the Duchess of Edinburgh.
Prince William delivered the speech during the ceremony
| GETTYJames, Michael and Carole Middleton were all present, but Kate's sister Pippa missed out.
Some 1,600 guests joined the royals for the event, which included individuals from across the UK who have given their time to support others and those in need.
This year's service focused on celebrating love in various forms, including family bonds, friendships, community involvement, and kindness shared between strangers.
The event combined traditional aspects with modern elements, aimed at welcoming guests of all faiths and those without religious affiliations.
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