The grieving father of Dreamworld victim Roozi Araghi found out about the tragedy from a news report.
Behrooz Araghi says his son, his son's partner Luke Dorsett, and Luke's sister Kate Goodchild travelled from their Canberra homes to Queensland for a wedding and decided to squeeze in a trip to the Gold Coast theme park on Tuesday.
The three were killed alongside Sydney-based New Zealand ex-pat Cindy Low when a raft carrying the four adults and two children flipped on Thunder River Rapids ride.
The two children, a 10-year-old boy and a 12-year-old girl, survived but lost their mothers.
Mr Araghi, who lives in Sydney, said his family learned of the tragedy via a news report.
"My son, my second son found out accidentally on the news. Wife saw the news, (she) went away," he told The Australian.
He said the family of siblings, Mr Dorsett and Ms Goodchild, must be experiencing unimaginable grief.
"We've lost one son - the mother of my son's partner lost two," he said.
Simon Araghi said the loss of his baby brother and his partner was hard to fathom.
"We are all in shock and mourning," he posted on Facebook.
Senator Sam Dastyari paid tribute to his friend Roozi and his father, saying they'd helped the senator's own family move from Iran to Australia.
"I'm devastated that such a caring, loving, sweet and sensitive friend has been lost," the senator wrote on Facebook.
ABC radio presenter Patricia Karvelas said she knew Roozi and Luke Dorsett, describing the couple as "the best and most loyal friends".
"They never missed one of my girls' birthdays. They never forgot to check in. Words fail me," Ms Karvelas tweeted.
Friend Douglas Robinson said both were amazing men.
"Canberra is a very small gay community, everyone knew them or knows someone who knew them," he said on Facebook.
Mr Araghi had worked at the Australian Bureau of Statistics and used to write music reviews for LGBTI website Same Same.
"The ABS is devastated by the tragic loss of Roozi Araghi, one of our dedicated, professional hardworking team members, who was very popular and well-regarded," ABS said.