The brother of murdered aid worker David Haines said he is haunted by the look on his face in video released by Islamic State (IS) militants.
Mr Haines was beheaded last September after being taken hostage in Syria in March 2013 while working for international relief agency Acted.
The 44-year-old father-of-two had been been helping refugees in a camp near the Turkish border when he was snatched by militants.
Mike Haines said the family had to keep his brother's kidnap secret for 18 months, which they found very difficult.
His brother's name emerged in the public domain early in September after he was shown at the end of a video of journalist Steven Sotloff's murder.
In an interview to be broadcast on BBC Radio Scotland on Sunday, Mr Haines said he is haunted by the look on his brother's face.
He told the BBC: "That day when David appeared in the background, that day when we realised that David had been identified, my stomach hit the floor.
"The image on David's face when he was witnessing Steven's murder - it wasn't horror at what was approaching him, it was horror at what was happening to Steven.
"The look - no matter where you go, no matter how much you try and not see that image - is with me all the time.
"In the deep, dark nights when I am not sleeping, I see that look on his face."
The recording was released two weeks after a clip appeared online showing the beheading of another American journalist, James Foley.
A video showing David's death was broadcast on social media 10 days after the Sotloff video.
In pictures: David Haines memorial
In pictures: David Haines memorial
1/8 David Haines Memorial Service
Mike Haines and Barbara Henning, wife of Alan Henning, at a memorial service for David Haines, who was murdered by Isis militants
2/8 David Haines Memorial Service
British Legion veterans arrive at Perth Congregational Church for a private memorial service held to commemorate David Haines
3/8 David Haines Memorial Service
Perth Congregational Church ahead of a memorial service to David Haines, the British aid worker beheaded by Isis militants.
4/8 David Haines Memorial Service
Bethany Haines, the daughter of David Haines, arrives at the Perth Congregational Church for her father's memorial service
5/8 David Haines Memorial Service
The order of service at Perth Congregational Church following a memorial service to David Haines
6/8 David Haines Memorial Service
Mike Haines and Barbara Henning have called for 'acts of unity' in the face of Isis threats, in a joint letter sent to the Guardian
7/8 David Haines Memorial Service
Pete Wishart MP (second left) and John Swinney MSP arrive at Perth Congregational Church for David Haines' memorial service
8/8 David Haines Memorial Service
Bethany Haines, daughter of David Haines with her boyfriend (name not given), leaving a memorial service to her father David Haines
Mr Haines said his brother and his family did not believe in paying ransoms.
"I have revisited every decision that was made and I would not change a single one because those decisions were made for the right reasons in the right way and that, no matter what we did, David's fate was sealed," he said.
Born in Yorkshire, David Haines was brought up in the Perth area and attended the local academy before serving 12 years as an aircraft engineer with the RAF.
He later took up humanitarian work and assisted aid agencies in some of the world's worst trouble spots.
Mike Haines wants his brother to be remembered for how he lived rather than how he died.
He said: "His love for his daughters. His belief in community. His belief in humanity. There is no nobler role in life than helping your fellow man when he is down no matter creed, religion, colour - David did that.
"So the work that he did, it stands for him."
The programme, titled Brothers: The David Haines Story, will be broadcast on BBC Radio Scotland at 10.30am on Sunday February 1 and will be available for a week afterwards on the BBC iPlayer.Reuse content