Unhappy end darkens this cartoon film (4,6,3,8)

I believe the answer is:

kind hearts and coronets

'film' is the definition.
(Kind Hearts and Coronets matches up with the definition film)

'unhappy end darkens this cartoon' is the wordplay.
'unhappy' indicates anagramming the letters.
'end'+'darkens'+'this'+'cartoon'='enddarkensthiscartoon'
'enddarkensthiscartoon' is an anagram of 'KIND HEARTS AND CORONETS'.

I've seen this clue in The Times.

Want a hint initially instead of a full solution? Install my app