Princess Charlotte's surprised reaction was caught on camera after Prince Louis' secret was revealed.
Princess Kate spoke about how her youngest son Prince Louis managed to keep a special Royal Ballet performance secret from his sister Charlotte at the Together At Christmas carol service.
The Princess of Wales shared details of the touching moment during a conversation with singer Paloma Faith at the annual festive celebration.
The secret involved a special performance by soloists from the Royal Ballet, knowing how much eight-year-old Charlotte loves ballet.
Princess Charlotte's surprised reaction caught on camera after Louis' secret revealed
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The nine-year-old princess's reaction to the Royal Ballet performance proved the secret was well-kept, as she appeared visibly delighted during the special act.
Kate enlisted six-year-old Louis to keep the surprise under wraps for his sister, testing the young prince's ability to maintain the secret for nearly two weeks.
The festive service brought together members of the Royal Family and notable guests for an evening of Christmas celebrations at Westminster Abbey.
Speaking to Paloma Faith at the event, the Princess of Wales revealed how she had tasked her youngest son with the special mission.
Princess Charlotte is a huge lover of ballet
ITV
"Can you keep a secret otherwise it won't be a surprise for Charlotte, who loves her ballet dancing," Kate recalled asking Louis.
The young prince proved himself up to the challenge, managing to keep the secret for an impressive duration.
"He has kept the secret for, what, nearly two weeks now," Kate shared with Faith.
"Very challenging," responded the singer. "For a six-year-old," the princess agreed, acknowledging the difficulty of the task for someone so young.
Princess Charlotte in awe watching the performance
ITV
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Princess Kate chatting to Paloma Faith during the concert
PADespite his impressive fortitude, Prince Louis nearly revealed the surprise on the morning of the service.
"And then this morning he said 'Mummy, please can I tell her - I'm bursting,'" Kate shared.
The princess explained how the excitement had almost overwhelmed her youngest son at the last moment.
"I did drop off and he really wanted to tell her. I think - hopefully - he's kept it," she added.
