Sergio Blanco Rivas and Estíbaliz Uranga Améraza were both former members of Mocedades , the group which represented Spain at the 1973 Contest with " Eres tú " , Estíbaliz is in fact the sister of lead singer Amaya Uranga . Both " Eres tú " and " Tu volverás " were written by prolific Spanish composer and lyricist Juan Carlos Calderón
1973 Contest
Eurovision Song Contest 1973
Tú volverás