Troubled by the worst conclusion that followed (6)
I believe the answer is:
tailed
'that followed' is the definition.
(I've seen this before)
'troubled by the worst conclusion' is the wordplay.
'troubled' becomes 'ailed' ('ail' can be a synonym of 'trouble').
'by' says to put letters next to each other.
'conclusion' suggests the final letters.
The last letter of 'worst' is 't'.
'ailed' put after 't' is 'TAILED'.
(Other definitions for tailed that I've seen before include "Dogged" , "Followed like rear appendage" , "Followed, tracked" , "as a dog at the end" , "Followed by private detective, having rear appendage" .)