Emily Lembo, Dan's daughter-in-law tells TMZ Dan died Sept 3 from an incurable brain disorder called progressive supranuclear palsy. We're told he battled the disease for 6 years, and over time, it took a huge toll on his memory, speech and motor skills.

Emily says Dan died peacefully at his home in New York, where he was surrounded by loved ones.

'Survivor' fans will remember Dan from season 21, which filmed in 2010. Dan made it all the way to the final five and was voted out on Day 37. Dan was a successful businessman and wore expensive alligator shoes during the competition.

Emily says he loved being on the show and getting recognized on the street -- he was very outgoing and will be remembered for his larger-than-life personality.

He was 75.