Beyonce unwittingly turned the spotlight on Princess Eugenie during her show in London on Monday (29Apr13) by reportedly asking the British royal to sing with her - not realising she was addressing an heir to the throne.

The Crazy In Love hitmaker attracted several famous faces as she kicked off her week-long residency at the U.K.'s capital's O2 Arena, including fashion designers Matthew Williamson and Patrick Cox, as well as actress Donna Air, who took her new boyfriend James Middleton, the brother of Catherine, Duchess of Cambridge.

Princess Eugenie was also at the concert, but the royal was left red-faced after she was picked to sing part of Beyonce's hit song Irreplaceable.

A source tells Britain's Daily Mirror, "It was hilarious - Eugenie was on the front row with Kate Middleton's brother, James, and his new girlfriend, Donna Air, plus designers Matthew Williamson and Patrick Cox. She was really excitable and filming the whole thing on her iPhone like any other fan.

"Beyonce clearly didn't recognise her so when it came to Irreplaceable, and the part where she picks on an audience member to join in with her, she simply chose the first woman she could reach. When Eugenie, who had gone bright-red, ducked down, Beyonce was forced to quickly fill in the missing words and find a new, willing victim. All Eugenie's friends were teasing her about her stage fright for hours afterwards."