Hayley, dressed in a white t-shirt and very sparkly (and amazing) jeans, and Taylor, in an equally sequined-out outfit, danced together and sang "Curious" at Gillette Stadium for Hayley's very first stadium performance.
Afterwards, Taylor posted a video of the surprise on-stage collab to Instagram, and wrote, "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."
She followed up with a few pictures of the performance, writing, "Hay & Tay looking like we're in a musical."
Meanwhile, Hayley shared some thoughts of her own on the performance on social media, excitedly writing, "DO NOT KNOW HOW TO COMPREHEND WHAT JUST HAPPENED. PLEASE LET ME KNOW. THANK YOU."
Hayley followed up with a more heartfelt post of her and Taylor rehearsing for the surprise moment. She wrote:
"It's really hard to put into words how I feel and what just happened. I feel overwhelmed. Taylor, you reached out to someone who dreams of being heard and understood. Thank you for giving me one of the biggest gifts of my life, opportunity. And thank you for showing me that these crazy dreams of mine are possible. I couldn't be more grateful. We keep climbing :)"
Hayley is currently on tour with Panic! At The Disco for their "Pray For The Wicked" Tour, and were also in town the same week performing at Boston's TD Garden.
Taylor is currently on her "Reputation" stadium tour, which finishes up in the US on October 6th, before heading to Australia, New Zealand, and then Japan. The tour wraps up in Tokyo on November 21st.
Photo: Getty Images