Australian mother Jillian Searle faced an agonising decision as a wall of water approached her on the Thai resort island of Phuket on Sunday.
Jillian Searle and her family are now safe in Perth
She had her two young children with her, but realised she would only survive if she let go of one of them.
"I knew that if I held on to both, we would all die," she told reporters. "I just thought I'd better let go of the one that's the eldest."
Fortunately all three survived, and are now back in their home city of Perth.
Moments before the tsunami hit, the Searle family had been enjoying breakfast near their hotel pool.
Mrs Searle's husband had just gone back into the hotel when water engulfed the area, and she found herself clinging onto her two sons, desperate to keep hold of them.
Still clutching her two-year-old son, Blake, she appealed to a woman nearby to grab hold of five-year-old Lachie - who cannot swim.
Although the other woman tried to hold on, she was forced to let go and he slipped into the water.
The boys' father, Brad, watched the scene helplessly from the balcony of their first-floor hotel room.
He found his wife and younger son soon after the water receded, and the family then went in search of Lachie.
"I was screaming, trying to find him, and we thought he was dead," Mrs Searle said.
Lachie was found two hours later, having been discovered by a security guard clinging to a door to keep his head above water.
"We are just so lucky to walk away with the small children I've got, one of whom can't even swim and is petrified of water - even the pool at home - and one who is a little baby," said Mrs Searle.
"I just can't believe they are still here."