Swingarm failure - torque arm mounting point

[kebab19]

Had a bit of an incident this morning.
Normal road riding conditions probably doing 50 or so at the time.
Pulled front & rear brakes to slow down, heard a fairly loud crack then realised that the rear brake pedal was solid and wasn't working anymore.  I was about 2 miles from home so limped back and then had a look in the driveway.
I was disturbed to see both the rear caliper and the torque arm had rotated up round the top of the swingarm.  I thought the torque arm securing bolt had either come off or broken but then took a look under the swingarm where the torque arm mounts  :eek Brake fluid all over the back wheel after the line got twisted round.
These swingarms are alloy so it can't be due to corrosion.  I have no idea how this could have happened, everything was secured safely.  Could it be down to the bluespot rear (or silverspot in my case)? Metal fatigue?
I realise some people will suspect I was acting an eejit, locking the rear at 80 or something, but this wasn't the case.  Sobering stuff....
Anyway, I now need a replacement swingarm, RHS chain adjuster and rear brake line now  and new pants