The magician, knows as "X", caused an eerie atmosphere when arriving on stage in a white mask and did not speak a word. Instead, a creepy voice played out from the speakers.
The magician stunned everyone when putting Ant and Dec's friendship to the test and performed a trick that seemed to reveal the hosting duo's telepathic powers.
Now, viewers have taken to social media to give their theories on who the mystery act really is.
Many believe it is magic act Elizabeth from the first episode of the talent show.
Elizabeth freaked out audiences with her impressive magic act the week before.
One fan wrote online: "I don't know what other people think but I think Elizabeth of Britain's Got Talent is also the masked magician #BGT."
A second agreed, adding: "Does anyone else think that Masked Magician is Elizabeth from last week on Britain’s Got Talent??? #bgt #bgt2019 #magic #maskedmagician #elizabeth."
And a third speculated: "Is this the same woman back from last week ? 😂 #BGT."
i dont know what other people think but i think elizabeth of britain's got talent is also the the masked magician #BGTI think Elizabeth of Britain's Got Talent is also the masked magician.
— Arran Jennings (@AzzerJ) April 14, 2019
— Sammy McHugh (@chimp1984) April 13, 2019
This the same woman back from last week ? 😂 #BGT
— A Game Of Skulls (@Game_Of_Skulls) April 13, 2019
The fan speculation stems from Elizabeth telling the BGT judges that she would be back soon, after she made it through to the next round of the competition.
Elizabeth terrified judge Amanda Holden during her trick, when she appeared to transform into an old woman who had died years ago.
She then told the audience: "The night's not over yet."
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