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.
triumphant
ADJECTIVE
1 Having won a battle or contest; victorious.
‘two of their triumphant Cup team’
postpositive ‘a comic fairy tale about innocence triumphant’
https://en.oxforddictionaries.com/definition/triumphant
https://en.wikipedia.org/wiki/Postpositive_adjective