How to save dying Sliver Princess eucalyptus tree?

[Bluetonge]

Dear Ms/Sir,

The Silver Princess (Eucalyptus Caesia) in my garden is mature and has always flowered normally including last year but this spring it has lost most of its leaves, many branches are dead and the bark is curling off the trunk. There is some spotting on the remaining leaves.

There has been no changes to its environmental conditions such as soil, watering etc.

Can you help me?

Thanks and kind regards,

Bluetongue