Image copyright Laura Palmer / BBC Image caption Capaldi's Someone You Loved is one of the year's biggest-selling singles

Lewis Capaldi packed out the BBC Music Introducing Stage as he played an unannounced set on the opening day of Glastonbury.

The star took to the stage at 13:30, playing Grace accompanied just by a piano, and the entire audience singing every word in unison.

As the song finished, Capaldi said he'd expected the crowd to walk away as soon as his name was announced.

"But you stayed, so thanks for that."

The brief, six-song set was Capaldi's Glastonbury debut, before a full set on the Other Stage on Saturday.

Media playback is unsupported on your device Media caption Lewis Capaldi performs Someone You Loved for BBC Music Introducing

He played the smaller BBC stage, which showcases new and unsigned acts, as a "thank you" for the helping hand they'd given him at the start of his career.

The star, whose debut album, Divinely Uninspired To A Hellish Extent, is the fastest-selling record of the year so far, later popped again on the Pyramid Stage to perform a cameo with Bastille, duetting on their song, Joy.

On the festival's main stage, Bjorn Again got things started with a hit-packed set of Abba songs.

They opened with the 1974 Eurovision Song Contest winner Waterloo, before racing through tracks like Mamma Mia, Gimme Gimme Gimme (A Man After Midnight) and SOS - which they mashed up with The Police's Message In A Bottle.

Image copyright Getty Images Image caption Bjorn Again have been playing Abba covers for 30 years - three times as long as the original band lasted

"We're here! We're really here!" said Carla Winters, who "plays" Abba star Agnetha Faltskog.

"I can't believe this is really happening," added her bandmate, known enigmatically as Benny Anderwear.

The tribute band, whose recreation of the Abba sound is spookily accurate, drew a huge crowd, who sang back every word, especially for the set-closer Dancing Queen.

Over on the Other Stage, MØ's songs about late night hedonism were curiously well-suited to the blazing heat of the midday sun - with the bouncy reggaeton groove of Red Wine prompting spontaneous outbreaks of dancing.

Then, during the first crush anthem Nostalgia, the Danish star threw herself over the barrier, and started singing from the middle of the mosh pit.

It was a performance of such infectious positivity that the star is certain to have won hundreds of new converts.

The rest of Friday's line-up includes Sheryl Crow, Lauryn Hill, Bastille, George Ezra, Pale Waves and Interpol.

Stormzy headlines the main stage from 22:15 BST, with live coverage on BBC Two and BBC 1Xtra.

Temperatures are expected to reach 28 Celcius during the day, and stewards are handing water to the audience during the day to keep people hydrated.

The festival is also giving out free sun lotion; and says it will open additional shaded areas if necessary.

Image caption Pyramid Stage meets Pyramid Stage hat

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