Donna Summer -- the Queen of Disco -- died this morning after a battle with cancer ... TMZ has learned.
We're told Summer was in Florida at the time of her death. She was 63 years old.
Sources close to Summer tell us ... the singer was trying to keep the extent of her illness under wraps. We spoke to someone who was with Summer a couple of weeks ago ... who says she didn't seem too bad.
In fact, we're told she was focused on trying to finish up an album she had been working on.
Summer was a 5-time Grammy winner who shot to superstardom in the '70s with iconic hits like "Last Dance," "Hot Stuff" and "Bad Girls."
TMZ has learned ... Donna died from lung cancer. Several sources are telling us Donna believed she contracted it by inhaling toxic particles after the 9/11 attack in New York City.
I was never a big fan of synthetic disco music, but Donna Summer always kept the heart in her songs.