Rocker Dave Grohl feared he had broken royal protocol when he greeted Prince Harry at an official function like a long-lost pal.

The Foo Fighters star was invited to perform a set at the closing ceremony of the Invictus Games in London in September (14) by the heir to the British throne, who had organised the event.

However, when it came to meeting him, the band joined a line-up of dignitaries but Grohl had no clue about the acceptable way of greeting royalty.

He tells British Tv programme The One Show, "We didn't know how to address him, (we didn't know) the etiquette, and so when I met him it's like, 'Hey man! What's up, dude!' and then the next person in line was (saying) 'Your Highness' and I didn't know what to do. But he was great, very cool... I think he might have called me 'dude', I can't remember. He was very cool."

More than 400 wounded servicemen and women took part in the games, which included archery and swimming events.