Flower of distinction

There's a large shrub next door to my home almost as large as a small tree. It has only one flower open with no sign of any further possibilities with no extra buds.
Quite unusual as it seems to be a healthy specimen.
I have pasted a standard postage stamp to one of its petals so one can gauge the size of the bloom.
No doubt there would be a botanical name applicable, but it appears that it maybe from the Camellia family.