Tabloid king is ruined (4)
I believe the answer is:
sunk
'is ruined' is the definition.
('sunk' can be a synonym of 'ruined')
'tabloid king' is the wordplay.
'tabloid' becomes 'sun' (The Sun, UK newspaper).
'king' becomes 'k'.
'sun'+'k'='SUNK'
(Other definitions for sunk that I've seen before include "Sent to bed" , "Gone under" , "ruined" , "Submerged" , "(Has) disappeared beneath the waves" .)