"He has the shoes of someone else."
Translation:El are pantofii altcuiva.
Altcineva is the nominative-accusative form. Examples:
Nominative: Altcineva mă iubeşte. = Somebody else loves me.
Accusative: Eu iubesc pe altcineva. = I love somebody else.
Altcuiva is the genitive-dative form. Examples:
Genitive (the above example): El are pantofii altcuiva. = He has the shoes of someone else.
Dative: Dă iubirea ta altcuiva. = Give your love to someone else.