The hostages in Islamic State execution videos appear calm because they do not realise they are about to die, according to a former captive.

French war reporter Didier Francois, who was released by the terrorists earlier this year, said that prisoners were threatened with execution ‘several times’ and IS militants carried out macabre mock crucifixions.

Commenting on why the hostages, including Briton David Haines, remained calm even seconds before their deaths, the journalist said: ‘They did not realise that this time it was the real thing’.

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Didier Francois, who was released by IS earlier this year, said that prisoners were threatened with execution ‘several times’ and were put through mock executions

Mr Francois said James Foley was treated worse than the other hostages because the militants found a picture of his brother - who is a member of the US armed forces - on his computer

Mr Francois, 53, of Paris-based radio station Europe 1, and three other French journalists were freed in April near the Syrian-Turkish border.

The French government has denied that a ransom of $18million (£11million) was paid to end their ten-month captivity, but many believe the cash was paid through middlemen, including private companies and Turkish secret agents.

Mr Francois revealed after his release that Foley was treated harsher than the other captives because the militants found a picture of his brother - who serves in military - on his computer.

Giving an insight into the physical and mental torture the hostages endured at the hands of the terrorists, the french journalist called Foley 'one of the pillars of the group,' who 'never cracked even under the most difficult conditions'.

'He was an extraordinary guy, an extremely nice companion in detention, very solid,' Mr Francois said in August.