My son, who's a keen Triathlete, came over for the week and brought his bike. "Dad - can you have a look at the crank, I think it's gone wrong":
I'm sure he'll claim it's massive power but I'm sure there's some defect somewhere that's the initial cause. Whatever, the damage is impressive.
Apparently this is not an unusual failure.
See here: Bikeradar, YouTube, YouTube (again), TrainerRoad forum for examples, or just put "Shimano Crank failure" or similar into Google
