Amelia Bambridge was last seen at a beach party in the early hours of 24 October.
"According to the people who are transporting her body, it's nearly 100 percent her, looking at her body's markings, including tattoo", Narin said.
"I have had the most horrific confirmation that my sister Amelia Bambridge was found and she is no longer with us", Bambridge's sister Sharon Schultes posted to Fb.
Her sister, Georgie, told CNN on Wednesday that Amelia had last contacted the family on October 23 when she messaged to say how fantastic her trip had been.
Deputy navy commander Tea Sokha said the authorities were tipped off about the body by fishermen who saw it. They both travelled to Cambodia before she went to Koh Rong. Around 150 people are taking part in the search for Bambridge who has not been seen since last Wednesday night when she attended a beach party on the island joined by tourists of various nationalities.
The charity said on Twitter: "We are aware of the very tragic news from Cambodia".
Bambridge's brother, father, and mother arrived in Cambodia on Sunday to join the search. "We are assisting her family".
The mystery deepened after police detained six men for questioning but they were found not to be involved and released. "Please respect the family's privacy at this hard time".
Volunteers joined almost 150 police officers and military personnel in searching for her on land and sea.
Friends and family held a vigil for her on Wednesday night and more than £16,000 was raised to help the family with their search efforts.
Chamroeun, the Preah Sihanouk provincial governor, said that while Bambridge's backpack being placed tidily on a rock close to the sea suggested she had drowned, an autopsy must be carried out to establish the exact cause of death.