The most likely explanation is frost damage if the plant is otherwise healthy - a sudden frost can cause this on buds and flowers, particularly if the plant is situated where it gets early morning sun.

Thanks Bamboo for the answer...yes it is on the patio where it gets the early morning sun.....so I will have to think where to move it to.

Doesn't even have to be frost....a heavy dew followed by morning sun can often cause this damage !!!

It looks like what we in the States call Camellia Blight--seems to be caused by cold, wet weather.