Calamity resulting from Diana's bloomer (8)
I believe the answer is:
disaster
'calamity' is the definition.
(calamity can mean a disaster)
'diana's bloomer' is the wordplay.
'diana's' becomes 'Di's' (Di is short for Diana).
'bloomer' becomes 'aster' (aster is a kind of flowering plant).
'dis'+'aster'='DISASTER'
'resulting from' acts as a link.
(Other definitions for disaster that I've seen before include "Sudden catastrophe" , "Event causing great damage" , "Star dies (anag)" , "complete failure" , "Terrible calamity" .)