It was Niall Horan's turn on Friday night and now Taylor Swift has thanked Robbie Williams for the "spectacular moment" when he joined her on stage at Wembley Stadium.
The US pop star, who is on her Reputation Stadium tour, brought Williams on stage on Saturday, to rapturous applause.
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She and Williams, who was wearing a Taylor Swift T-shirt, then performed a duet of his hit song Angels.
Swift has now posted a message on Instagram thanking Robbie.
"Still processing how special last night was, thank you London for two incredible nights at Wembley Stadium," she said.
"I'll NEVER forget the sound of the crowd when Robbie Williams showed up to sing Angels, that was UNREAL!!
"Thank you to Robbie, that was such a spectacular moment and it meant so much to so many people, including me."
Williams shared a photo of the pair together on social media, saying: "What an honour to sing with you tonight @taylorswift.
"I've got a proper crush. THANK YOU THANK YOU THANK YOU x."
On Friday night, Niall Horan joined Swift for her first concert at the venue.
Swift surprised her thousands of fans at the packed arena as she welcomed the One Direction star for a duet of his solo hit Slow Hands.