The 23-year-old singer surprised fans at her third 'Red' tour gig in the city by bringing out the former 'The Voice' mentor as her surprise guest.
Taylor told the crowd: ''One of my favourite things about coming to the UK is that I've discovered bands that have become some of my favourites. There's a band I first heard when I came over here ... They have a really great lead singer - it's Danny O'Donaghue from The Script!''
The pair performed a duet of the Irish band's hit song 'Breakeven' to rapturous applause, with Taylor thanking the crowd for being the ''craziest yet''.
The country starlet - who was supported by new boy band The Vamps - kicked off the show with her 'Red' album opener, 'State of Grace', before launching into popular title track 'Red'.
Amid costume changes and gravity-defying stage antics, Taylor powered through her best songs from her latest album, including 'I Knew You Were Trouble' and grand finale 'We Are Never Ever Getting Back Together', as well as a handful of old favourites like 'Mean' and 'Love Story'.
The singer also explained her fascination with the colour red, which featured prominently in the elaborate theatre-themed staging and her various sparkly get-ups.
She said: ''I bet a lot of you are wondering why there's a fixation on this one colour. When I was writing my last album I came up with the idea of comparing feelings to colours and there was this one that represents all the emotions; love, hate, jealousy, passion ... If you had to pick one colour that's intense, fleeting, beautiful and sad all at once when we fall in and out of love it would be red.''
Taylor's 'Red' tour continues on Monday, February 10 and Tuesday, February 11.
To coincide with her residency at The O2 Arena, the British Music Experience - which is situated inside the O2 - are showcasing select items from Taylor's wardrobe alongside photographs by Christie Goodwin in a pop-up exhibition.
Admission to 'Taylor Swift: A Photo Experience' is included within the price of a museum ticket, and costs just £4 to ticket holders for her O2 shows during the duration of her residency.
The exhibition runs until 23 March.
He also slapped a jet-lagged Taylor Hawkins.
The acclaimed performer had just cancelled touring due to a battle with cancer.
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