The likely reason for Princess Eugenie's mysterious disappearance from Princess Kate's carol service has been revealed.

The princess didn't join dozens of fellow Royals who rallied around the Princess of Wales at her Christmas carol service in central London this week.

The 'Together At Christmas' carol service, held at Westminster Abbey, marked Princess Kate’s first solo event of the year after she underwent a major abdominal surgery in January and announced she had been diagnosed with cancer.

Kate announced she would be gradually returning to royal duties after her preventative chemotherapy treatment ended in September.

After a rough year, the theme of this year's carol service was announced as a celebration of those supporting others in need, with a focus on the importance of love and empathy.

Kate was joined by her husband Prince William and their three children - Louis, six, Charlotte, nine, and 11-year-old Prince George.

Other royal attendees included the Duchess of Edinburgh, Lord Frederick Windsor, Zara Tindall and a pregnant Princess Beatrice.

But her sister Princess Eugenie did not attend, along with the King and Queen. While the reasons for Eugenie's absence are unknown, it is likely due to her decision to split her time between the UK and Portugal with her husband and two sons, August and Ernest.

Her husband, Jack Brooksbank, is believed to working in Portugal with Michael Meldman's Discovery Land Company.

A royal source previously told Express.co.uk: "The villa in Portugal is more an investment than anything else and construction hasn't even been completed yet".

They added: "It hasn't been purchased as a new home, but more as a holiday retreat and something they can put their money into to protect their assets."

The public were given a rare insight into Eugenie's life in Portugal earlier this year after the 34-year-old royal revealed that her sons, three-year-old August, and one-year-old Ernest "love swimming", despite her being "scared" of the ocean growing up.

The service, held on Friday evening, saw the princess stop for a chat with guests who were giving the readings including actors Richard E Grant, Downton Abbey star Michelle Dockery, Sophie Okonedo, nominated for an Oscar for her role in the film Hotel Rwanda, and Olympic swimming champion Adam Peaty.