Guillaume Lekeu was a promising young composer mentored by Cesar Franck who contracted typhoid fever and died the day after his twenty-fourth birthday. I claim no great knowledge of him or his works, and in fact the piece I am going to link you is the only one of his that I've heard. It's his Adagio for String Orchestra, a beautiful and melancholic work written after Franck's death, and an excellent demonstration of just what was lost when he died.