Ruler in the last month in hospital (6)
I believe the answer is:
sultan
'ruler' is the definition.
(sultan is a kind of ruler)
'last month in hospital' is the wordplay.
'last month' becomes 'ult' (I've seen this before).
'in' indicates putting letters inside.
'hospital' becomes 'san' (I've seen this in other clues).
'ult' placed within 'san' is 'SULTAN'.
'in the' is the link.
(Other definitions for sultan that I've seen before include "Turkish ruler" , "Chicken" , "Muslim ruler" , "Ottoman emperor" , "One governs" .)