An affair with one of the Spanish invaders, we’re told (5)
I believe the answer is:
amour
'an affair' is the definition.
(amour can mean a love affair)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for amour that I've seen before include "French lover" , "Romantic affair" , "Affair of the heart" , "Love affair - loved one" , "20 [AFFAIR]" .)