See that little black line under that weld?
Not good news unfortunately. Crack-o-rama.
Best bit is that because I bought the frame privately (albeit new) it's not covered by the manufacturers warranty. They may be able to come to the party with a discounted frame of some description, but it's still $$$.
The crack itself it still hairline, so I'm hoping that a mate of mine who is an engineer is going to be able to gusset and weld it - and the result, while not original, should be stronger than original.