I thought I'd better put you out of your misery and fess up as to what the mystery flower is. It's on our catalpa tree at the front of the house (Jan got it right!). Jack started the tree from a seed and this is the first year it's bloomed.
No pictures today, because we have company & I'm doing this on the fly. Had the day at our CQTeer meeting and exchanged some pretty cool stuff. Pictures will follow - hopefully tomorrow!