One wouldn’t succeed the Spanish queen (5)
I believe the answer is:
loser
'one wouldn't succeed' is the definition.
'the spanish queen' is the wordplay.
'the spanish' becomes 'los' ('the' in Spanish).
'queen' becomes 'er' (abbreviation for Elizabeth Regina).
'los'+'er'='LOSER'
(Other definitions for loser that I've seen before include "One vanquished" , "One failing regularly" , "Roles for the defeated" , "One frequently failing" , "A failure, also-ran" .)