Kate Middleton and Princess Charlotte shared a heartwarming piano duet at the "Together at Christmas" carol service, playing "Holm Sound."

Just hours after Kate Middleton and Princess Charlotte's surprise piano duet aired, the mom and daughter joined the royal family on Christmas as they headed to church.

Princess Kate's 10-year-old daughter, Princess Charlotte, played the piano at her mother's side in a pre-recorded portion of the televised concert at Westminster Abbey. The royal duo performed "Holm Sound" by Erland Cooper during "Royal Carols: Together at Christmas."

It's a merry Christmas indeed, especially if you happen to be a fan of the British royal family. This morning, we were gifted with an appearance from all of our royal favorites, including Kate Middleton,

The mother-daughter duo taped a performance inside Windsor Castle for the television broadcast of the Princess of Wales’s Christmas carol.

Princess Charlotte joined Princess Kate for a royal duet on Christmas Eve as part of the special "Royal Carols: Together at Christmas."

The Princess of Wales and Princess Charlotte shared a surprise (and poignant) moment at the royal Christmas carol service.

Kate Middleton and Princess Charlotte teamed up for a surprise piano duet at her fifth annual “Together At Christmas” carol service earlier this month. The mother of three, 43, released a clip of a rendition with her daughter, 10, of “Holm Sound” by Erland Cooper via social media on Wednesday following the U.K.’s ITV broadcast at 2:25 p.m. ET.

Princess Diana adored the spirit of Christmas, but she often struggled with some royal traditions. In fact, there was one element of the celebration that weighed on her deeply.