coup de main - noun
\ˌkü-də-ˈmaⁿ
Definition of coup de main : an attack that achieves complete surprise.

Watch: Gracie Abrams and Taylor Swift perform 'Us' live.

Celebrating the release of her new album 'The Secret Of Us', Gracie Abrams popped up as a surprise guest during Taylor Swift's Eras Tour show in London last night to perform their duet 'Us' together live.

Watch some clips of the performance below...