Harry Dunn's heartbroken twin brother couldn't leave the family home for six weeks following his death .
Niall, 19, couldn't bring himself to step outside after discovering his beloved sibling had been killed close to RAF Croughton, an American spy base in Northamptonshire, back in August.
He was struck by a car driven by Anne Sacoolas, 42, the wife of a US diplomat - who has since returned to America and claimed diplomatic immunity.
She is said to have hit football fan Harry head-on after driving on the wrong side of the road.
The teenager's mum Charlotte Charles, 44, and dad Tim Dunn, 50, are expected to land in America on Sunday to put pressure on Donald Trump to force the mum-of-three to return to the UK and answer questions.
Distraught Charlotte has told the Daily Mail of the full impact the political battle is having on the family.
"It still feels unreal," she said. "But when you wake up in the morning, if you manage to get any rest at all, and that gnawing grief feeling in the pit of your tummy hits you, you know it is.
"The boys were really close. As youngsters they were inseparable and always up to mischief.
"That broke me, really broke me. ‘It was the first time in six weeks I’ve really cried — really, really cried. There have been little breakdowns but we've all had to try to be stoic for Niall.
"Bless his heart, he’s said it really upsets him to see us upset so we’ve had to be strong for him."
Now the parents are flying to the US this weekend to fight for a face-to-face meeting with President Trump .
Earlier this week Trump waded into the international diplomatic immunity row and was condemned for his clumsy analysis of Harry’s death.
But in a follow up press conference the US leader softened his stance, revealing Sacoolas was “being spoken to” and that “we’re trying to work something out.”
They will continue their fight for justice by giving interviews on major news channels.
Lawyer Radd Seiger, who is representing the family, is understood to have arrived in Washington DC last night for talks. He said: “Bringing her back to Britain is our priority.”
Prime Minister Boris Johnson revealed that this is unlikely.
He said: “America is reluctant to allow its nationals to be tried overseas. We’ve got to keep working to get justice for Harry.”
