Strange upset after gang followed the French primate (4-6,5)

I believe the answer is:

ring-tailed lemur

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'strange upset' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how they can define each other.

'gang followed the french primate' is the wordplay.
'gang' becomes 'ring' (synonyms).
'followed' becomes 'tailed' (I've seen this before).
'the french primate' becomes 'lemur' (lemur is a kind of primate. I am not sure about the 'french' bit.).
'ring'+'tailed'+'lemur'='RING-TAILED LEMUR'

'after' is the link.

Can you help me to learn more?

I've seen this clue in The Times.

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