Princess Beatrice sliced open Ed Sheeran's face with a sword while attempting to "knight" James Blunt as a party prank.
Sheeran, 25, was rushed to hospital after the 28-year-old Princess Beatrice of York— the eldest daughter of Prince Andrew and Sarah Ferguson — swung the ceremonial blade over her shoulder without realising he was behind her, The Sun reports.
Sheeran, who is making a new album, has happily showed off the scar after the party at Prince Andrew's home, The Royal Lodge at Windsor.
The accident happened earlier this month at the Royal Lodge in Windsor, home to the Duke of York.
Prince Andrew was away on business in Mexico but Beatrice's mum Sarah Ferguson, who has staged mock knighthood ceremonies in the past, was at the private dinner party.
The following night Ed made no attempt to hide his injury as he attended a gig at the Shepherd's Bush Empire posing for pictures with fans.
Twitter users asked what had happened and speculated wrongly that he must have been drunk.
A source explained: "Ed had been invited to dinner as a guest of Princess Beatrice.
"They all sat down and there were 20 or so guests."
James Blunt and his wife Sofia Wellesley were among the guests and after dinner James joked that he would love a knighthood.
The Princess said she could arrange it and fetched a ceremonial sword.
As James knelt down Beatrice said "Arise Sir James" but instead of tapping him lightly she swung the sword over her shoulder not realising Ed was standing right behind her.
She caught Ed on the face lacerating his cheek which began to bleed.
According to news.com.au mock knighthood ceremonies are nothing new for the Royal Family.
In 1990 Bea's mum Sarah, now 57, amazed party guests in New York when she "knighted" a dog.
The Duchess of York bent down, dubbed the pet Sir Rutherford and tapped him on either side of his ears with a breadknife.
Those being knighted for real kneel before The Queen as they are dubbed, lightly touched on the shoulder with a sword.
Prince William recently knighted Rod Stewart at Buckingham Palace — and when the Queen met the rocker later that day she asked him: "Did he do it OK?"