The crossword solution for UNFORGETTABLE SINGERS is COLES, which refers to the American singing duo comprised of sisters Natalie and Ella Coles. The sisters are best known for their soulful R&B music, which has earned them numerous awards and accolades. They have released several albums and singles, and have toured extensively throughout the United States and Europe. Their music has been featured in films, television shows, and commercials, making them one of the most recognizable and beloved singers of the 21st century.