The American tourist who was devoured by a shark in Indonesia is believed to have died of a “medical issue” while diving, her friends told The Post on Monday – revealing that she was an experienced deep-sea diver who ” really enjoyed life”.

Colleen Monfore, a retired mother of two from Holland, Michigan, was enjoying her dream vacation — a seven-week diving trip with her husband, Mike — when tragedy struck on Sept. 26, family friend Rick Sass said.

Just days into the trip, 68-year-old Monfore disappeared during a group dive around the island of Pulau Reong, north of Timor-Leste and off the coast of southwestern Maluku Regency. Two weeks later, fishermen in Timor-Leste caught the shark – and cut human remains from its belly more than 70 miles from where she disappeared.

Authorities were able to identify Monfore from the body’s fingerprints, according to Sass, a longtime friend who was in close contact with the family during their harrowing ordeal.

“We don’t believe it was a shark attack. Mike believes she suffered a medical issue in the water,” Sass told The Post.

Sass and his wife Kim – who ran a dive shop together for more than 40 years – examined photos from the dive, spoke to Mike in detail about the incident and reviewed data from his dive computer.

The friends insist that Monfore, who Rick Sass said apparently became separated from the group when rough water forced them to turn around, was not killed by a shark. She was about 24 feet down and probably had half a tank of air left, he said.

“There was a downward current at the turnaround point, but it was manageable,” Kim Sass wrote in a Facebook post. “I have easily done more than 1,000 dives with this lovely woman… I don’t think it was the environment, let alone a shark, that took her life.”

Rick Sass added, “They have taken countless diving trips with us over 30 years. Bali, Philippines, Bikini Atoll, whatever.

“She knew what she was doing.”

Mike Monfore was already an avid scuba diver when he met Colleen in high school in her home state of South Dakota, and she, too, soon fell in love with the ocean.

They had two children and eventually four grandchildren, but never stopped traveling the world and exploring the seas together. “They were both retired and really enjoying life,” Rick Sass said.

“We used to call her ‘Saint Colleen.’ She was an amazing woman,” he added. “She loved nature and animals. I know she would never have wanted a shark to be blamed for this tragedy.”

He noted that shark attacks on divers are extremely rare.

“And sharks aren’t like that. We dived with hammerhead sharks, tiger sharks and bull sharks. You have to show them respect and be careful, but they won’t just attack you.”

According to the Florida Museum of Natural History’s International Shark Attack File, there were only 69 confirmed unprovoked shark bites worldwide last year, and 94% of them occurred on snorkelers, waders and surfers. The remaining 6% are assigned to the “Other” category.

It is not yet clear how exactly Colleen Monfore died. Grisly photos from the crime scene show the shark in question cut open – with human remains in a black wetsuit nearby.

“The shark was caught but its health was not normal. I thought it had swallowed plastic or a fishing net,” the fisherman said, according to Asia Pacific Press. “It was cut open to find the problem and inside were the remains of a woman.”

Rick Sass said her husband is struggling not only with her death, but also with bringing his wife’s remains home.

“He hardly slept, partly because he was on the phone with Indonesia, which means a time difference of 12 hours,” he said. “He’s taking calls in the middle of the night and talking to us during the day and he can’t sleep just because of this terrible thing that happened.”

Indonesian authorities said an investigation was underway.