Beyonce and Sir Paul McCartney have reportedly become gym buddies.

The pop star and Beatles legend have both been in Southern California recently, with Beyonce delivering a surprise performance at the annual Coachella Valley Music and Arts Festival in Indio, California last weekend.

UK newspaper The Mirror reports the pair started working out together during their stays at the Four Seasons Hotel in Los Angeles, about 130 miles west of the city.

And Sir Paul, 71, apparently shocked fellow guests when he waltzed in with Beyonce, 32, after a recent sweat session.

'They strolled in laughing and joking like old pals and hopped on the treadmill. Paul had a remarkably good pace,' a source said.

'Beyonce then got off to join her trainer, who was trying to get Paul to join in.

'The pair then moved on to the studio where they stretched and did some gentle Pilates. People think it was a coincidence but it isn't the first time they have been to the gym together,' the insider added.

Sir Paul, who's gearing up to resume his Out There Tour, hasn't been shy with his praise for Beyonce.

He recently said she's one of the acts he checks out when he's preparing to hit the road to make sure he's up to date on all the new trends.

''If I'm gonna do a tour I like to go and see what other people are doing. I don't wanna bring my tour out and be amazingly old-fashioned," he recently told NME magazine.

''So if people are going, 'Oh man Beyonce, she was killer!' I like to go there and go, 'Yeah, we can do better than this,'' he said.

Beyonce meanwhile surprised fans at Coachella last weekend when she hit the stage with sister Solange.

The diva is also said to be planning a 20-date tour with husband Jay Z, kicking off towards the end of June.