If you look at the end that's broke off you can see the connector with the little silver circlip the same clip that's on the other end where it plugs into the expansion tank. Plugged into that clip on the radiator end is the radiator outlet that's broken off the radiator.
It's part of the radiator and cannot be replaced, the pipe is fine but the radiator is buggered!
I've just looked at mine and the radiator can be removed easily enough.
It could have been knocked at some point and weakened it, or excessive pressure in the cooling system could have caused the radiator to split or it could even be a case of someone breaking it in the past and glued it back on.
Anyway any good garage will be able to replace the radiator and check the cooling system is working properly.
Did you not get a coolant level warning appear on the dash?
