Police said they mistakenly told Lily Hooper's family she was alive, after the 18-year-old's body was found in dense bushland in Nattai National Park, in NSW's Southern Highlands.
An SES volunteer found her about 11.30am on Thursday, but a communication breakdown led to incorrect reporting to her family, NSW Police Assistant Commissioner Joseph Cassar said.
"(The family) were informed (of) initial information the searchers believed she was alive, and that's what was communicated," Mr Cassar told reporters.
"Within eight-to-10 minutes we were able to give them an update which was a more accurate account."
Ms Hooper disappeared on August 12 after going on a hike.
The teenager from Oakdale, in Sydney's southwest, did not return that evening and could not be contacted on her mobile phone, triggering a wide-scale search.
Her car was discovered at the Bonnum Pic trailhead the same night she went missing, but Mr Cassar said the teenager was found a long way from her vehicle.
"I can't give you the exact distance but ... it wasn't on a clear walkable track," the assistant commissioner said.
"It's thick, dense bush and a lot of it is steep cliff area."
The senior officer apologised to Ms Hooper's family for the miscommunication and the loss of their beloved daughter.
"Every one of the investigators and the searchers, whether they were volunteers or paid personnel, hoped for a more positive outcome," Mr Cassar said.
"If we were able to provide them more detailed information on that first report, I can tell you that would have been the case."
Her parents expressed relief to the media before being told their daughter may not be alive.
NSW Premier Chris Minns initially told a parliamentary hearing Ms Hooper had been found alive before later interrupting proceedings for a second time to apologise for the error.
"I've got some terrible news … but it seems as if the early advice was wrong and Lily's body's been found and she's been found deceased," the visibly distressed premier said.
The premier later issued a statement apologising to the family.
"I genuinely believed I was sharing good news," Mr Minns said.
"I am profoundly sorry to think anything I said may have added to their heartbreak at an already devastating time."
Mr Cassar said he was not aware who informed the premier of the incorrect details of the discovery.
Mr Minns earlier told the hearing Ms Hooper had been found alive with half a bottle of water on her and thanked NSW Police, SES, the Australian Defence Force and hundreds of volunteers who helped with the search effort.
Mr Cassar said he did not know where the detail about the water bottle had come from.
Prime Minister Anthony Albanese told parliament Ms Hooper had much more to offer the world.
"Lily Hooper has been taken from her family, her community, and our nation, far too young … losing a young one is an unspeakable tragedy," he said.
Opposition Leader Angus Taylor, who is the local member for the Hooper family, said any parent who learned of the teenager's death would hug their children tighter than usual.
The House of Representatives had a moment of silence for Ms Hooper before Question Time.
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