Radiator blowing up on the rollers?

They started my car up on the rollers and during the run the rad decided to self destruct.
The top pipe has ripped off and broken off.
The rad top half exploded.
Rad is goosed.

I will be dropping my spare gti-r rad down there.

What the fcuk could have caused this?
No other damage to the car, will I will inspect when i am down there tomorrow?

Sticky radiator cap not relieving pressure in to expansion tank would be my guess?

or blown head gasket / cracked head

Don't say that Bob..
Nah it was the pipe top hose connector that snapped.
The rad did look old to be fair.

Picture example below of what happened.

Hopefully just old radiator that gone brittle as plasticity boiled out of it over the years.
Cap issues tend cause minimal failure as pressure build up from heat expansion is gradual thus failure more gradual.
Ring sealing on combustion pot head gasket blowing direct to water way can make impressive mess . Seen that take out a cheap fibreglass/carbon bonnet too lol
Imagine having a fuel injector and spark plug in your rad :-)