Lady Gaga joked that veteran crooner Tony Bennett runs rings around her on stage as she met Prince Harry at a charity gala tonight.
The prince charmed the pop royalty ahead of the concert, and Gaga declared she thinks Harry is "fantastic".
The trio chatted ahead of a performance by Lady Gaga and Tony Bennett to support WellChild, a charity that supports children with life limiting conditions which the Prince is patron of.
Gaga told the Prince: "We are so happy to be here tonight and be of any help."
Explaining how he and Gaga collaborated on their album, Cheek to Cheek, veteran crooner Bennett, 88, said: "I heard her personally and said we have to get together."
Harry said: "I can't believe you have the energy I don't know how you do it."
But Gaga laughed and replied: "He runs circles round me. Wait until we get on stage."
She added: "We think you are fantastic. And thank you for bringing it here so we can support you."
Bennett told the Prince he was friends with his late mother Lady Diana.
He said: "Your mum was a good friend of mine. I did many benefits with her."
Harry replied "That's fantastic."
The Prince said it was a shame such few children from the charity could be at the concert because it was in the evening, and Gaga said she could meet them another day.
Hundreds of people had waited outside the concert hall in London to catch a glimpse of the popstars and the Prince.
After he greeted the musicians, Harry then met two teens helped by the charity and their nurses, who he later watched the concert with.
Flynne Ewart-Biggs, 15, from Islington north London, has been having treatment for a brain tumour for 18 months and receives the support of WellChild.
She spent the evening in the royal box with the Prince and other nurses and families who receive the help of the charity.
Flynne said her nurse Diane Miles is "a friend as well as a nurse".
She added: "It's the first time I've met the Prince. It was fairly easy to talk to him to be honest because he led the conversation.
"He asked me if I liked Lady Gaga. He didn't say if he was a fan but I'm sure he is."
She revealed she had kept tight-lipped and not told her friends about her VIP date with the Prince at the concert.
Laughing, she added: "I don't know if I'll get up and dance in the royal box."
Abby Gardner, 17, from Clacton-on-Sea, suffers from Wolfram Syndrome which causes diabetes, deafness and vision problems.
Asked how it felt meeting the Prince, she said: "It means a lot. I know he is patron of WellChild and he does a lot. It was nice to meet him and say thank you for everything."
Patrick Vallance, head of research and development at sponsors GSK, said: "He said he wished more children supported by WellChild could be here. And he speculated on what the audience wants, whether its Lady Gaga or Tony Bennett fans."
WellChild chairman John Evans said: "He's incredibly impressive with the children.
"He'll get down on their level. One of the things the parents appreciate is when the prince gets down on his knees to talk to their children."
He said the charity was lucky to have the patronage of the prince.
The concert raised more than £100,000 to support the charity.
The charity's chief executive Colin Dyer said: "This is a huge event for us."