What is "guercoeur"

Guercœur is an opera in three acts by the French composer Albéric Magnard to his own libretto. It was first performed posthumously at the Paris Opéra on 24 April 1931, though it had mostly been written between 1897 and 1901. The composer died trying to save his house from the invading Germans at the beginning of World War I in 1914 and the score was partially destroyed in the resulting fire. Magnard's friend Guy Ropartz reconstructed the missing sections so the opera could be staged. The music shows the strong influence of Wagner.