Rye Hunt's family say he was loyal, loving and an "infuriating!" brother after his body was found on a Brazilian beach.
Clinical tests confirmed the body washed ashore at Marica was that of Mr Hunt, who went missing in Rio on May 21.
"We are understandably heart-broken," Mr Hunt's sister Romany Brodribb said.
"Rye was the youngest member of our family and was known for being loyal, loving, generous, cheeky, and as a brother, totally infuriating!
"Thinking about life without him is unfathomable. He will be very missed by us all."
His partner Bonnie Cuthbert, who went to Rio to join the search for him, said she felt blessed to have shared her past five years with her "beautiful Big Bear".
"We have been so lucky to have found and loved each other so deeply. The love Rye and I shared will remain within both of us, forever."
The 25-year-old backpacker went missing on May 21 after he separated from his travelling companion Mitchell Sheppard at the Rio airport.
They had an argument after the two took what is suspected to be a highly potent hallucinogen known as NBOMe.
The family said on Facebook they were disappointed they weren't given the opportunity to share the sad news before it was announced to the media.
"We are understandably grief-stricken as we come to terms with the events of the past two weeks and will not be available for comment," a statement said, adding the family asked for their privacy to be respected.
Foreign Affairs Minister Julie Bishop said on Twitter the family was told immediately after the Brazilian authorities confirmed the test results overnight, and she answered a question from the media at midday.
Ms Bishop said the Australian government would work with the family to provide whatever support was possible.
"We will continue to work with the Brazilian authorities to determine how this death came about," she told reporters in Melbourne on Saturday.
Mr Hunt's family thanked the Australian Embassy and Consulate, Department of Foreign Affairs and Trade, and Brazilian police for their help in finding him and supporting the family.
The search for Mr Hunt started on social media when Ms Brodribb and her family could not contact him after he was last seen at the airport.
Police released CCTV footage showing Mr Hunt at the airport and a search led them to an apartment he booked for three days.
It then emerged he likely took a local drug that caused extreme paranoia and anxiety, and may have swum to an island 900 metres off the coast of Rio.
Mr Hunt's uncle Michael and Ms Cuthbert travelled to Rio to help run the search.
His body washed ashore on June 8 in Marica, just outside of Rio.
