Prince Harry has enlisted none other than the Queen to star in a brilliantly funny Twitter video exchange with President Barack Obama to promote the Invictus Games.

In the biggest royal spoof since the Queen pretended to jump out of a helicopter with James Bond for the London 2012 Olympics opening ceremony, the Prince shows a video of Barack and Michelle Obama throwing down the gauntlet to the British team.

"Hey Prince Harry," says Mrs Obama. "Remember when you told us to bring it at the Invictus Games?"

President Obama, standing next to her, says: "Careful what you wish for!" before a serviceman behind him says "Boom!" as others pull faces.