Leslie Palethorpe was one of 15 people who died from carbon monoxide poisoning after two drums of fuel were thrown into the downstairs foyer of the Fortitude Valley nightclub and set alight about 2am on March 8, 1973.
The following day was his sister Helen's 14th birthday.
Her statement was read in the Coroners Court in Brisbane where the third sitting of the inquest into the attack started on Monday.
Disgraced former police detective Roger Rogerson and murderer Vincent O'Dempsey who has been accused of involvement in the firebombing are expected to be called to give evidence.
Ms Palethorpe said she was excited in the lead-up to her birthday about the prospect of seeing her brother, a soldier then based in Townsville, who was coming for training at the Enogerra army base.
She last saw him in January as he left Brisbane after visiting for Christmas and his son's christening.
"I have the vision still of him hanging out the window waving goodbye, beeping all the way down Anzac Avenue," she said in a statement read out to the court on her behalf.
On the day of the firebombing Ms Palethorpe was pulled from class without being told why and taken in a cab to her aunt's house.
She continues to have flashbacks of her devastated parents finding out their first child was dead.
Her mother was "hysterical and beside herself", while Ms Palethorpe's father heard of his son's death on the radio.
"He never recovered from hearing this horrible news this way," Ms Palethorpe added.
"Seeing both my parents in this state is forever etched in my mind."
Ms Palethorpe said her birthday was bittersweet after her brother's death.
"I never had another happy birthday again until my five children threw me a surprise 60th party."
She has also never found closure or recovered, particularly as there is no answer to the question why the attack occurred.
"It has broken me," she said.
John Andrew Stuart and James Richard Finch were convicted of murder over the attack on the Whiskey nightclub and sentenced to life in prison.
Both men have died - Stuart in 1979 and Finch in April last year in the UK where he was deported after 15 years behind bars.
Despite the men being jailed for murder, the full extent of the circumstances causing the deaths had never been "satisfactorily established", an earlier court hearing was told.
Rumours have persisted that other people were involved in what was Australia's worst mass murder case until Tasmania's 1996 Port Arthur massacre.
Rogerson - who is behind bars in NSW for murder - is the only person still alive who signed a confession made by Finch days after the firebombing.
The inquest before coroner Terry Ryan was ordered in 2017 after the attack was mentioned in a trial which convicted O'Dempsey and Garry Dubois over the deaths of Barbara McCulkin and her two daughters in January 1974.
That trial was told the killings may have been motivated over fears Ms McCulkin would try to implicate O'Dempsey in the firebombing.
Dubois was found dead in his Maryborough prison cell in June last year, but O'Dempsey sat in court for some testimony during the first two sittings of the inquest.
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