Dio, che nell'alma infondere
"Dio, che nell'alma infondere" was a duet from the 19th century opera Don Carlos, composed by Giuseppe Verdi.

The Doctor performed "Dio, che nell'alma infondere" aboard the  for an audience of Voyager crewmembers and a number of fascinated Qomar in 2376. 

He later gave small holograms of him singing the same song to Qomar admirers, even singing a duet with his small holographic self. ()

Background information 
 Robert Picardo did not actually sing the vocal parts above. They were voiceovers by the famous opera singer Agostino Castagnola, as was The Doctor's performance of "Rondine al nido" later in the episode. 
 Robert Picardo performed this piece on stage when he played the character of Max in a production of Ken Ludwig's Lend Me a Tenor at the Pasadena Playhouse in 1992.

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