It seems not everyone who attends a Beyoncé concert knows the lyrics to her songs.

But during a London concert, Beyoncé reportedly embarrassed royalty.

The 31-year-old singer often has segments in her shows where she turns the microphone over to an audience member and lets them finish a song lyric in front of concert-goers. Beyoncé turned the microphone over to Princess Eugenie during her "Mrs. Carter World Tour" while performing the hit single “Irreplaceable.”

It is unclear if Beyoncé recognized who the royal was. Princess Eugenie, who is sixth in line to the throne, said nothing. The daughter of Prince Andrew and Sarah Ferguson was supposed to say, “to the left, to the left” but instead left Beyoncé to find another willing participant.

"It was hilarious -- Eugenie was in the front row with Kate Middleton's brother, James, and his new girlfriend, Donna Air, plus designers Matthew Williamson and Patrick Cox," a source told British newspaper the Mirror.

"She was really excitable and filming the whole thing on her iPhone like any other fan.

"Beyoncé clearly didn't recognize her, so when it came to ‘Irreplaceable’ and the part where she picks an audience member to join in with her, she simply chose the first woman she could reach,” the source continued.

When Eugenie, who had gone bright-red, ducked down, Beyoncé was forced to quickly fill in the missing words and find a new, willing victim.

"All of Eugenie's friends were teasing her about her stage fright for hours afterward."

Eugenie has not commented on the incident.

Beyoncé’s tour is set to hit 15 European countries before arriving in the U.S. on June 28. Beyoncé’s last major tour, in 2009, was the “I Am ..." world tour.