A former army sergeant who survived a devastating IRA bomb blast has stabbed his two children to death before killing himself in a countryside bridleway.
The bodies of Michael, 51, Ben, seven, and Freya Pedersen, six, were found next to a Saab 900SE convertible car in a lane near Andover, Hampshire, on Sunday.
Mr Pedersen was a former army sergeant in the Household Cavalry unit that was hit by an IRA nail bomb in Hyde Park in 1982, it has been reported in the Daily Telegraph.
On Monday, the children's maternal grandfather, William Clifford, 67, from Buckinghamshire, speaking outside his daughter Erica's home in Ashford, Middlesex, said: "We are obviously devastated and what we would ask is that you respect our privacy in this matter.
"It is extremely distressing and that is all I want to say."
The police spokesman said the coroner has been informed and post- mortem examinations are due to take place later.
Detective Superintendent Tony Harris said: "We are currently investigating the circumstances surrounding this terrible incident and are working to establish what has led to these tragic deaths.
"We are treating this as an isolated incident and we do not believe anyone else was involved.
"The families of Michael, Ben and Freya have been informed and specialist family liaison officers from Hampshire Constabulary, and officers from Surrey Police, are working with them to provide support and keep them updated as the investigation progresses.
"Our thoughts are with the family and friends of those involved at this extremely difficult time and I would ask that they be allowed to come to terms with what has happened in a dignified and respectful way."
Detective Superintendent Tony Harris, of Hampshire police, said that the "tragic incident" happened during a visit to Mr Pedersen's father during an arranged visit with his children from his estranged wife.
Harris said that Surrey Police were considering referring the case to the Independent Police Complaints Commission (IPCC) because of some previous contact with Pedersen.
Harris said the mother of the two children had alerted Surrey Police at 7pm on Sunday after Pedersen, of Chertsey, Surrey, failed to return with the children at the arranged time of 5pm.
He said he believed the deaths happened at some point during the afternoon.
Harris said: "A Home Office pathologist visited the scene and at this time it appears the children suffered fatal stab wounds and Pedersen took his own life shortly afterwards."
He added: "They were visiting relatives in Andover, which is nearby.
"It was the father of Pedersen, the grandfather of the children."
Describing the incident, he added: "Any scene you go to with children involved is distressing for the officers, we have given them support and they continue to receive support.
"It is very tragic, it's a dreadful loss of life, one of the most tragic cases I have had to deal with."
Harris said police were in the process of tracing the family of Pedersen, who had two other children from a previous relationship, when his estranged wife raised the alarm.
He added that he was not looking for anyone else in connection with the deaths.
The bodies were found lying behind the car, he said.
He added: "It's very isolated and there was a person walking yesterday who notified us to the presence of the vehicle but I do not anticipate anyone else would have seen anything."
The children's mother was informed by a family liaison officer and was being provided with support, he said.