In English it is most usual to place an adjective before the noun that it modifies - a cold day, a triumphant rider, but rarely you will find adjectives placed after the noun - they are said to be postnominal or postpositive. These chiefly appear in a restricted set of situations. Certain adjectives are found more often, and triumphant is one.
His formidable enemies defeated him on almost every side, yet in the end he emerged triumphant.
1 Having won a battle or contest; victorious.
‘two of their triumphant Cup team’
postpositive ‘a comic fairy tale about innocence triumphant’