Alpha male's last UV treatment is chaos (8)
I believe the answer is:
'is chaos' is the definition.
'alpha male's last uv treatment' is the wordplay.
'last' indicates one should take the final letters.
'treatment' indicates anagramming the letters (the letters must be processed or treated).
The final letter of 'male' is 'e'.
'alphaeuv' anagrammed gives 'UPHEAVAL'.
(Other definitions for upheaval that I've seen before include "Major disturbance" , "Disruptive disturbance" , "Violent change or disturbance" , "Turbulence" , "State of violent disturbance and disorder" .)