ITV News has learnt Harry Dunn’s family have been told the foreign secretary was only made aware of the case after Anne Sacoolas had left the UK - 21 days after the crash which killed the 19-year-old.
Nine months on from the crash and a week ahead of a judicial review case management hearing, Harry Dunn’s family say the revelation raises more questions over the Foreign Office’s handling of the case and have repeated their calls for Dominic Raab to resign.
In April, ITV News saw an FCO briefing note copied to Dominic Raab’s private office outlining what had happened three days after the crash on August 30.
The note raised concerns over the potential for “some very unpalatable” headlines.
Harry Dunn's mother Charlotte Charles said: "We have never trusted Dominic Raab from the start.
"We have met with him and his advisers numerous times yet never once did they mention that he did not have control of the situation last September, that he just did not know about it until after Mrs Sacoolas left.
"That just can’t be right.
"But if it is, why have the FCO left it to the 11th hour to say that the captain of the ship was off somewhere else while the ship was burning?
"Why after all our meetings did they not tell us that and just offer it up to us now.
"He owes us a duty of candour which he has never once complied with.
"We only wanted the truth from him, nothing else.
"Whether he knew or not, and I refuse to believe he didn’t know, he has to resign or be sacked."
ITV News Correspondent Neil Connery explains how the revelation raises more questions over the Foreign Office’s handling of the case
Harry Dunn was killed when his motorbike was in a collision with a car allegedly driven by Anne Sacoolas - the wife of a US intelligence officer based at RAF Croughton in Northamptonshire - on August 27 last year.
The US government claimed she had diplomatic immunity and she and her family left the UK on September 15 returning to America.
The US embassy informed the Foreign Office the day after she had left.
In December Anne Sacoolas was charged by the Crown Prosecution Service (CPS) with causing death by dangerous driving.
But the US government is refusing to extradite her insisting she had diplomatic immunity at the time of the crash.
Harry Dunn's family say they understand the US government's decision not to waive the diplomatic immunity it claims Sacoolas had, along with the decision to return her and her family back to America was taken at senior levels in Washington.
The Dunn family representative Radd Seiger said: "Mr Raab and the British government are in a total state of disarray over their handling of the Anne Sacoolas affair last year.
"The FCO initially said that Mr Raab was not aware of the case at the time of the now infamous reception at Ambassador Johnson’s residence in London.
"They have now said something completely different, that he wasn’t even aware until after Anne Sacoolas had gone on September 15."
He added: "It is utterly inconceivable that Mr Raab was unaware of Harry until after Mrs Sacoolas had gone.
"Mr Raab has to go.
"Let’s just give him the benefit of the doubt for one second and agree that his team kept him away from what was happening.
"We know his private secretary received a detailed note about the case on August 30.
"We know that she was being kept abreast of developments.
"Every senior member of Mr Raab’s team was aware of what was going on, anticipating that there would be unpalatable headlines?
"If he really did not know despite all that we are going to have accept that his entire leadership team kept one of the most important cases away from their boss.
"If true then what does that say about his control over his ship and his relationship with his team?
"The question that should worry all of us, regardless of our politics, is whether this is cock up or conspiracy, we are simply not safe in Mr Raab’s hands as the main person responsible for representing our country’s interests on the world stage."
The Foreign Office said "We remain clear with the US that the refusal to extradite Anne Sacoolas amounts to a denial of justice, and that she should return to the UK.
"The case is of the highest priority for the Foreign Secretary who continues to raise the case with the US Government."
Shadow Foreign Secretary Lisa Nandy told ITV News: "It either appears that the foreign secretary was not across his own brief in relation to this important case - or that he hasn't been truthful with the House of Commons about what he knew and when.
"Both of those things are extremely serious - we have to get to the bottom of this, not just because it's important to get justice for Harry, but because every single person in this country is entitled to know that if something like this happens to them, the Government is on their side."