Clint's sister, Taylor, broke the news ... "It is with great sadness, to tell you that my family has lost my best friend and older brother Clint on the morning of January 11th. Please respect our family's privacy as we try to cope with this great loss."

Taylor did not provide information on the cause of death. She said they'll be sharing details on the service.

The 34-year-old had his own slogan on the show -- "Villians gotta vill."

Nick Viall competed against Clint on the show and reminisced, calling Clint "very kind," adding, "Just heard about the passing of Clint Arlis. I got a chance to get to know Clint a little after our time on Kaitlyn's season and I always enjoy [our] time and conversations."

Clint was an architectural engineer. He lived in Chicago.

Clint was 34.