She'd gone to watch headline act - and friend - Taylor Swift.

So it's perhaps fitting that actress Emma Watson should be seen downing a quick pint at London's British Summertime Festival on Saturday.

The actress was seen guzzling down her beer in full party spirit as the 25 year-old singer capped a weekend of performances in the sun.

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Thirsty work: Emma Watson should was seen downing a quick pint at London's British Summertime Festival on Saturday, where she watched pal Taylor Swift

Seen with a group of female friends, the actress was clearly having a good time as she soaked up the atmosphere in the capital.

With her hair scraped back into a casual bun and sporting a full face of make-up, she'd clearly opted for festival glamour to mark the occasion - including some sexy denim hotpants and leather boots.

And, while stood in a ray of light, the Harry Potter actress quenched her thirst for both beer and pop culture simultaneously.

Bottoms up! Seen with a group of female friends, the actress was clearly having a good time as she soaked up the atmosphere in the capital

Putting on a leggy display: The popular actress certainly cut a seasonal figure at the weekend

Looking good: With her hair scraped back into a casual bun and sporting a full face of make-up, she'd clearly opted for festival glamour to mark the occasion

Plait'll do nicely! The British actress sported a hippy-inspired braid in her long hair

Refusing to take her eyes off the stage, she looked on - rapt - as the 1989 singer wowed music fans and critics alike.

Just hours earlier Emma had re-tweeted Taylor's message about America's gay marriage act, which was implemented via the Supreme Court at the weekend.

'And you can want who you want... Boys and boys and girls and girls,' she posted to Twitter, which suggested there was extra reason to celebrate.

Better the denim you know: The Paris-born star wore the type of hotpants Kylie Minogue would appreciate

Sharing the same stylist? Emma and her pal wore strikingly similar looks for the British Summer Time gig

Good times: Wearing a Breton-striped top with a pair of jeans, the British screen star was laughing and joking with pals at the open-air show

Stylish: Emma braved horizontal stripes for the evening outing - and looked fab

Carefree: Emma was also spotted dancing, laughing and joking with her mixed group of friends

Wearing a Breton-striped top with a pair of jeans, the British screen star was laughing and joking with pals at the open-air show.

Clearly getting carried away in the moment, she was also spotted dancing and posing for selfies with her mixed group of friends.

Together, they certainly seemed to embody the sassy pop which Taylor is so keen to front.

Rapt: Refusing to take her eyes off the stage, she looked on as the singer wowed music fans and critics alike

Strutting her stuff: Emma flaunts her perfect pins as she navigates the audience at Hyde Park

Get down on it: The Bling Ring star couldn't resist dancing to the much-hyped music show

Pretty: The actress looked beautiful - even despite keeping it casual for the annual gig

Not that Emma was the only celebrity in the crowd, of course.

Among the stars in the audience were British fans Emma Bunton and Melanie Chisholm - both of former Spice Girls fame - as well as television presenters Emma Willis and Tess Daly.

As a treat for US star Taylor, the crowd were warmed up by her very good friend Ellie Goulding on the night.

Ellie - who appears in Taylor's most recent music video for Bad Blood - delivered an impassioned performance to get the fans ready, jumping around the stage with high energy.

Busy crowd: Emma couldn't help but survey the thousands of people who'd attended the live set

Smile for the camera! Emma and her friend strike a pose in a photo opportunity

VIP access: The Harry Potter actress was able to watch the set from the side of the stage in a safe enclosure

Not the only celeb: Among the stars in the audience were British fans Emma Bunton and Melanie Chisholm - both of former Spice Girls fame - as well as television presenters Emma Willis and Tess Daly

As if that wasn't enough, festival goers were also treated to a surprise appearance from Taylor's gal pals Kendall Jenner, Karlie Kloss, Gigi Hadid, Cara Delevingne, Martha Hunt and Serena Williams.

Taylor concluded her show surrounded by a gaggle of famous female friends for an encore to remember.

The close girlfriends even dined out together before the London performance, hitting Notting Hill on Friday night for a catch up.

After a fleeting stay in London, Taylor is off to Dublin this week as she continues to promote her album 1989 with its accompanying sell-out tour.

Support act: Just hours earlier Emma had re-tweeted Taylor's message about America's gay marriage act, which was implemented via the Supreme Court at the weekend

Quality control: Emma and her pal apply some quality control to the photographs they've taken

Fancy another pint? Emma looks ready to fresh herself with another drink as she parties in the warm weather

Mwah! The friends pucker up for a comedy pose as they record the evening on their smart phones

Capturing the moment: Emma and two girlfriends cosy-up for a selfie at the concert