Christos Dritsas had been sitting in one seat on a high-speed train bound for Seville.
Minutes before the crash, the 18-year-old moved into the seat his older brother had left empty. The seat he abandoned was destroyed.
Christos, his brother Marios, 21, and their mother survived the deadly collision south of Madrid, in which a high-speed train slammed into a stationary train.
The Spanish newspaper El País put the death toll at 69, with about 100 people injured.
Spain's transport minister called it "inexplicable" that the moving train had been allowed to continue despite a red signal.
Rescue work was continuing, and the high-speed line linking Madrid with Andalusia remained suspended.
The family spoke to El País from a hospital in Toledo.
They had flown into Madrid on Saturday to see Seville. Marios and his mother had gone to the cafe car for breakfast and were waiting for their order when the impact hurled them into the air.
"Suddenly, time stopped," Marios said.
Passengers slammed into one another as the dining car left the tracks and tilted to a halt at an angle of about 30 degrees.
For several seconds there was a terrible roar, he said, and the car filled with the smell of earth.
They shouted for Christos. He was alive.
Their mother, her arm in a sling and her collarbone broken, let her sons do most of the talking. "I'm still in shock," she said, weeping over her phone as her sons held her.
A local volunteer drove the family from the wreckage to a nearby village before they reached the hospital.
Where language failed, they said, staff communicated with gestures and treated them with great kindness.
It is Spain's third rail disaster this year.
In January, two high-speed trains collided near Adamuz, in Córdoba province, killing more than 40 people. Days later, a commuter train derailed near Barcelona.
For Greeks, the story strikes a painful chord.
In February 2023, a passenger train and a freight train collided head-on near Tempi, in central Greece.
Fifty-seven people were killed, many of them university students returning from a holiday weekend. It was the deadliest rail disaster in Greek history.
That crash, too, was blamed on failures in signaling and safety systems. It set off some of the largest protests Greece has seen in years, and the victims' families are still demanding accountability.
One grieving mother, Maria Karystianou, has since founded a political party.
So when Greeks read of a mangled train, a red signal that should have stopped it, and a family reunited in the wreckage by the luck of a changed seat, many think of Tempi.
The Dritsas family said they planned to return to Madrid.