Taylor Swift and Hayley Kiyoko. Picture: Instagram
Taylor Swift was joined on stage by surprise guest Hayley Kiyoko at her Boston gig on Thursday night.

The 28-year-old star - who has had the likes of Niall Horan, Robbie Williams and Selena Gomez perform at her shows this year - wowed fans with a rendition of 'Curious' with the 'Girls Like Girls' singer at the packed out Gillette Stadium - the rising star's first-ever experience playing to a crowd that size.

Alongside a video of the duet, Taylor wrote on Instagram:"UM @hayleykiyoko THAT WAS INSANE!.

"Thank you so much for coming to surprise the crowd tonight at @gillettestadium - THAT WAS SO MUCH FUN!!!! So stoked this was your first stadium performance, and you absolutely killed it [sic]"
Taylor previously heaped praise on Hayley for her "brave" coming out story.

The 'Delicate' hitmaker said: "We should applaud artists who are brave enough to tell their honest romantic narrative through their art, and the fact is that I've never encountered homophobia and she has.

"It's her right to call out anyone who has double standards about gay vs straight love interests."

Meanwhile, Taylor has topped The Top 20 Global Concert Tours list.

The 'Love Story' singer's 'Reputation Stadium' tour's average box office gross per city beat the likes of The Rolling Stones' No Filter Tour, Beyonce and Jay-Z's 'On The Run II' and former rival Katy Perry's 'Witness' run.