Strangely, Pope told lies about one for so long (6-3)
I believe the answer is:
toodle-pip
'so long' is the definition.
(I've seen this before)
'strangely pope told lies about one' is the wordplay.
'strangely' indicates an anagram.
'lies about' indicates putting letters inside.
'one' becomes 'i' (Roman numeral).
'pope'+'told'='popetold'
'popetold' anagrammed gives 'toodlepp'.
'toodlepp' going around 'i' is 'TOODLE-PIP'.
'for' is the link.
(Other definitions for toodle-pip that I've seen before include "Goodbye (dated)" , "Take care" , "Farewell (informal)" , "Farewell remark - dipole top (anag)" , "so long" .)