Pierre Korkie, a South African teacher, held by al Qaeda militants in Yemen, died along with American photojournalist Luke Somers, a day before he was due to be freed after more than 18 months in captivity.
Relief group Gift of the Givers said in a statement on its website: “The psychological and emotional devastation to (his wife) Yolande and her family will be compounded by the knowledge that Pierre was to be released by Al-Qaeda tomorrow.”
The group helped negotiate the release of Mr Korkie’s wife, Yolande, after they were kidnapped by al Qaeda in the Arabian Peninsula (AQAP) in the Yemeni city of Taiz in May 2013.
Mrs Korkie was told on the morning of her husband’s death: “The wait is almost over.”
Arrangements had been put in place to fly Mr Korkie out of Yemen under diplomatic cover following negotiations.
“It is even more tragic that the words we used in a conversation with Yolande at 5.59 this morning was ‘the wait is almost over’,” the statement added.
“Three days ago we told her ‘Pierre will be home for Christmas’. We certainly did not mean it in the manner it has unfolded.”
Those close to the family said the militants demanded a $3m (£1.9m) ransom for his release.
President Barack Obama said the raid was authorised because information “indicated that Luke’s life was in imminent danger”.
“Based on this assessment, and as soon as there was reliable intelligence and an operational plan, I authorised a rescue attempt,” Mr Obama said.
“I also authorised the rescue of any other hostages held in the same location as Luke.”
Imtiaz Sooliman, founder and head of Gift of the Givers, said he did not blame the US for Mr Korkie’s death.
He told a news conference: “American troops in the attack, well of course I am not blaming them, because Americans have their own hostages as their interest.
“South Africans, we have our own hostages as our interest, we all have our own interest. They have their interests, we have our interests.
“And whatever has happened has happened, you know, I mean, there is no bad feeling towards anyone.”