On Friday evening the illusionist entered a plastic box hanging from a crane where he'll attempt to survive without food for 44 days - that's just over 6 weeks.
All a trick?
Blaine says during that time he'll only be able to drink water fed to him through a tube.
The box measures just 2.1m by 2.1m by 0.9m and is hanging near Tower Bridge in London.
With him inside he's just got blankets, a mat, a backpack with a diary in, pens, nappies, moist tissues and lip balm.
Some people might think Blaine will cheat, but he said: "There will be no trickery and no means of escape."
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