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Hard to tell for sure with the crankset still on, but it's definitely sheared fully off along the circumference and come clean off, the outside part is hanging round the axle like a ring. Whether there is a jagged edge to get a drift or flat-head screwdriver blade on I can't quite see at the moment, but if not looks like the thinking is hacksaw blade is the way to try,so I'll give that a go Monday.
Hang on. Is it sheared off like this, which is what I had in mind when I answered:
or do you mean it's sheared along the circumference so there's a whole ring left in there? In that case, I agree with chiroshi.