Also a backing group? (4)

I believe the answer is:

abba

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'group?' is the definition.
(pop group)

'also a backing' is the wordplay.
'also' becomes 'abb' (I can't justify this - if you can you should give a lot more credence to this answer).
'backing' says to put letters next to each other.
'abb'+'a'='ABBA'

Can you help me to learn more?

(Other definitions for abba that I've seen before include "Palindromic Swedish pop group who sang ` `Waterloo' '" , "6 24 113 [SCAN-DIN-AVIAN] band" , "camel-hair coat" , "Swedish pop music group" , "Form of address to deity" .)

I've seen this clue in the Evening Standard.

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