Kept talking, heartlessly betrayed (6,2)

I believe the answer is:

ratted on

'betrayed' is the definition.
('rat on' can be a synonym of 'betray')

'kept talking heartlessly' is the wordplay.
'kept talking' becomes 'rattledon' (to rattle on is to talk incessantly).
'heartlessly' says to hollow out the word (remove centre letters).
'rattledon' with its centre removed is 'RATTED ON'.

I've seen this clue in The Telegraph.

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