An inquest to establish exactly how he came by his death opened at Morier House this morning.
It heard that the woman, who had remained on shore, raised the alarm after realising that her brother – a strong swimmer who regularly swam in both the sea and at Les Quennevais Sports Centre – was in difficulty.
A man on a paddleboard found Mr Callias, pulled him out of the sea onto his board, and began to perform CPR on him while on the water.
Pictured: The inquest took place at Morier House this morning.
A Jersey Seafaris RIB picked up a mayday signal, went to the scene and took both men aboard their vessel.
Mr Callias was taken to the shore, where an ambulance was waiting and he was taken to hospital. However, despite further attempts to revive him by paramedics during the journey, he was pronounced dead on arrival.
The inquest concluded that Mr Callias had an “asymptomatic” heart condition – meaning that there had been no previous indications of it – and that he appeared to be physically fit.
Assistant coroner Cyril Whelan said: “It is likely that Mr Callias suffered a cardiac incident which left him incapacitated.”
Describing the people who had tried to rescue him, he added: “The fact that these were strangers helping other strangers is to be highly applauded.”
Mr Whelan expressed his condolences to Mr Callias’s family.