Aretha Franklin, the self-taught piano prodigy, vocalist and songwriter who first conquered the charts in the late ’60s and never relinquished her throne, has died, her publicist confirms to the Associated Press. She was 76.

The Queen of Soul had struggled with her health for years. A source told PEOPLE Monday that Franklin had taken a turn for the worse and that her death was “imminent.”

“She has been ill for a long time,” the longtime friend told PEOPLE. “She did not want people to know and she didn’t make it public.”

A musical phenomenon who crossed musical, racial and gender barriers, Franklin began her vocal career as a teenager, singing gospel hymns in her father’s Detroit church. From these humble beginnings she scaled to the very heights of stardom, scoring her first national chart-topper in 1967 with a searing version of “Respect.”

Since then, the artist has notched 77 Hot 100 chart entries, and earned an astounding 18 Grammys out of 44 nominations. In 1987, two decades after her first No. 1, Franklin became the first woman to be inducted into the Rock & Roll Hall of Fame, and was later named the Greatest Singer of All Time by Rolling Stone.