Britain's Got Talent viewers took to social media in their dozens after noticing how the magician did her trick.

Magician Alexandra Burgio ... They claimed it was "a simple card switch" undetected by most, and that's how she got the right card seemingly chosen at random by the audience.

One viewer posted: "All that build up to a simple card switch." Another agreed ... Alex has also found further fame as part of celebrated magician duo Penn and Teller's US TV series Fool Us ...