Sudden Clematis collapse - C. 'Rouge Cardinal'

I have a stunning Clematis 'Rouge Cardinal' growing up an arch in the garden, it's been covered in flowers as usual so far this summer.

Unfortunately 3 days ago the flowers all wilted over the course of an afternoon. The leaves similarly affected today. There are no outward signs of disease, the leaf colour is still good, watering is careful and the C. alpina on the other side of the arch remains, to date, unaffected.

I'm in the UK, does anyone have any ideas please? I can only think there is something eating the roots.

Sometimes they wilt - keep watering like you normally would.

Thanks for your answer.

The plant is definitely showing signs of dying now with no change to the usual regime.

I would still continue to water. All too often a clematis will die back and then come back a year or even 2 years later....

Thanks for your help.