What on earth has happened here ?

[Elasticatedwaist]

This azalea was here when we moved in 2 years ago , looking fine. It’s now like this.
there are two others next to it that look ok and the front bit of it still looks green.

Lack of water? The weather has been very hot, with little rain ( in my area South East anyway ) there is obvious die-back, which probably won’t recover.