Catastrophic crank failure.

[35cab]

I thought I would share a couple of photos. French block 4" crank in my 35. Whilst on a trip in August I felt a vibration, couldn't work it out, when car got to around 65 vibration went away. 200 miles into my 350 mile drive home to Scotland, had to slow down for roadworks then all hell broke loose.
Undignified return on back of recovery truck.
Pulled the engine last week, could see no obvious problem, checking for crank play float noticed a discrepancy between measurement on the front and at the rear, undid rod cap, ouch! (pic 1) crank out and this is what I found (pic 2)
JB weld ? :-)
I need to work out how this happened.
Gordon.