Former Welsh county formed in 1974 from most of Monmouthshire and part of Breconshire (5)

I believe the answer is:

gwent

(Other definitions for gwent that I've seen before include "Region of SE Wales" , "former Welsh county" , "part of Wales once" , "Preserved county of Wales" , "Blaenau - is a Welsh county borough" .)

I've seen this clue in The Independent.

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