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Instead, Caroline was joined by her children Charlotte, Pierre and Andrea, as well as as Princess Alexandra - her 11-year-old with Ernst.
And if the 54-year-old royal was upset at the absence of her husband, she wasn't showing it.
Dressed in a bright blue dress with a wide-brimmed straw hat, the princess looked delighted that her brother's big day had finally rolled around.
Commentators had expected Ernst to stay away from the celebrations. He hasn't accompanied his wife to an official event since 2009.
It is thought the couple have come to an agreement which allows them to lead separate lives while still remaining married.
A divorce was expected by the press after the German aristocrat was pictured kissing a mystery woman in Thailand over Christmas 2009 while Caroline spent the festive season alone with her children at a Swiss ski resort.
It had the potential to be one of the most costly divorces in history, as the prince is worth an estimated £5 billion and his wife would have been entitled to half.
But a divorce was not forthcoming, and Caroline maintained a dignified silence.
She even supported Ernst at his 2010 court case, appearing as a witness for his defence.
A Kenyan nightclub owner accused the German aristocrat of striking him during an argument, which had taken place ten years previously, about loud bar music.