'90 Day Fiancé' Star David Murphey Dead at 66

'90 Day Fiancé' star David Murphey -- who was best known for appearing on "90 Day Fiancé: Before the 90 Days" -- has died ... this according to his family.

The reality star's family issued a statement on his Instagram account Wednesday ... where they confirmed the TV personality died last week in Las Vegas, Nevada after "experiencing health issues over the last several years."

Sources with direct knowledge tell TMZ ... David had been sick with liver cancer, which he was diagnosed with over a year ago. We're told David also had been facing a number of other health issues, too. His cause of death is currently unclear.

Per sources, David had undergone over 13 surgeries in the last year ... and was scheduled to go under the knife again before his passing.

Despite his health issues, David was still actively seeing his family and friends in the week before his death ... but we're told he was "very frail and unwell." Sources say he had lost a lot of weight and often complained about not feeling well.

David, who was a veteran, small business owner, and software engineer, had recently retired from his position at the Clark County Treasurer's Office.

His family remembered him best as a "fierce" animal advocate, especially for cats ... and noted that David "always made an effort to adopt cats and give them a good loving home."

They encourage his followers to honor David's memory by donating to The Animal Foundation in Las Vegas in his name.

They continued ... "His time on ['90 Day Fiancé'] allowed him to connect with viewers, see the world, and share his experiences with his thousands of followers on Instagram. He will be deeply missed by his family, friends, and fans."

David's family asked for privacy "during this difficult time."

Fans of '90 Day Fiancé' will remember David from his controversial relationship with Ukrainian girlfriend Lana ... who DM notably dated online for 7 years before ever meeting. While David and Lana eventually became engaged on the show, they never got married ... splitting after their appearance on the TLC hit.

David is survived by his 2 sisters and his cat, Gamera.

He was 66 years old.