Taylor Swift knows how to keep her fans on their toes.
The 28-year-old singer is currently touring the UK on her Reputation World Tour, and last night she brought out a special guest to entertain the crowd on her first of two nights at Londons Wembley Stadium.
Before Niall Horan took to the stage, Taylor teased the surprise on Instagram to get her fans even more excited for the show.
Soundcheck at Wembley Stadium with this guy @niallhoran THANK YOU for surprising the crowd tonight!!! @GarethCattermole @hogieaaa @GettyEntertainment, Taylor captioned a slideshow of pictures of herself and the One Direction hunk having fun during rehearsals on Instagram.
The cheeky Irish popstar hit the stage with his pal Taylor to perform his worldwide smash-hit Slow Hands.
Fans rushed to social media during the concert to share their excitement about the surprise moment.
Earlier this month, Taylor took time out of her show to pay tribute to the victims of the Manchester Arena bombing.
The star was performing at the Ethiad Stadium in the city when she thanked fans for their incredible resilience to keep dancing and to keep the innocence and the joy and excitement.
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She told the crowd: Concerts are supposed to be about to innocence and joy and excitement and escaping things that stress us out, and what happened over a year ago was to try and steal that excitement and joy and escape, and ever since then youve shown such strength and youve shown you will never let anyone forget those victims,
And youve shown you have such incredible resilience to keep dancing and to keep the innocence and the joy and excitement.