Sir Paul McCartney and Dave Grohl are great friends – so it was only right he showed up to support him at Glastonbury! (Picture: BBC)

Now, Foo Fighters have their fair share of famous fans, but it doesn’t really get more famous than Sir Paul McCartney.

The Beatles icon was spotted side of stage as Dave Grohl and co. rocked out in their surprise Glastonbury set on Friday.

Eagle-eyed viewers noticed Sir Paul, 81, clapping and singing along, as cool as ever.

Also loving the tunes was his wife, Nancy Shevell, 63, who Sir Paul married 11 years ago.

‘Why didn’t this fellow get up for a cheeky number?’, one Twitter user joked, tweeting a screengrab of the Liverpudlian star.

Another tweeted: ‘@foofighters can’t be a bad feeling when your mate @PaulMcCartney is side of stage to watch you surprise the Glastonbury crowd at 6.15pm’.

‘Oooh @PaulMcCartney at side of stage there!’, another spotted.

Sir Paul and Foos frontman Dave, 54, are actually close friends, so it’s no wonder he wanted to cheer them on from the Pyramid Stage.

Dave has said on many occasions that he learned to play music by listening to The Beatles’ records, and he takes every chance he’s given to honour their legacy.

Over the years, Sir Paul has appeared in Dave’s documentary, given his daughter piano lessons, played drums for the band, and even inducted Foo Fighters into the Rock & Roll Hall of Fame.

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Sir Paul and Dave Grohl go way back.