The Queen supported EU withdrawal in the run-up to the referendum, it has been claimed.
Laura Kuenssberg, the BBC's political editor, said she was told about the alleged comment months before the eventual appearance of The Sun's "Queen backs Brexit" headline in March.
The front page story caused one of the biggest rows of the referendum campaign, leading to a successful complaint to press regulator Ipso by Buckingham Palace, which said it was "misleading".
The Sun stood by its story, saying it had two sources for the claim that the Queen had "let rip" at then Deputy Prime Minister Nick Clegg about Europe at a lunch at Windsor Castle.
Mr Clegg has named then Justice Secretary Michael Gove as the source of the story, but Mr Gove has never confirmed the allegation.
Ms Kuenssberg said that her "jaw hit the floor" when an unnamed contact told her that the Queen had told a private lunch that she could not see why Britain could not simply leave the EU.
The BBC political editor told BBC Radio 4's Today programme: "In a casual chat with one of my contacts, they said, 'Do you know what? At some point this is going to come out, and I'm telling you now and I don't know if the BBC would touch it, but the Queen told people at a private lunch that she thinks that we should leave the EU'.
"Apparently at this lunch she said, 'I don't see why we can't just get out. What's the problem?'
And a row ensued. "My jaw hit the floor. Very sadly, I only had one source. I spent the next few days trying to prove it. I couldn't find the evidence.
"Lo and behold, a couple of months later, someone else did. Of course then ensued a huge row between that newspaper and the Palace over what had really been said or not said.
What experts have said about Brexit
What experts have said about Brexit
1/11 Chancellor of the Exchequer Philip Hammond
The Chancellor claims London can still be a world financial hub despite Brexit “One of Britain’s great strengths is the ability to offer and aggregate all of the services the global financial services industry needs” “This has not changed as a result of the EU referendum and I will do everything I can to ensure the City of London retains its position as the world’s leading international financial centre.”
2/11 Yanis Varoufakis
Greece's former finance minister compared the UK relations with the EU bloc with a well-known song by the Eagles: “You can check out any time you like, as the Hotel California song says, but you can't really leave. The proof is Theresa May has not even dared to trigger Article 50. It's like Harrison Ford going into Indiana Jones' castle and the path behind him fragmenting. You can get in, but getting out is not at all clear”
3/11 Michael O’Leary
Ryanair boss says UK will be ‘screwed’ by EU in Brexit trade deals: “I have no faith in the politicians in London going on about how ‘the world will want to trade with us’. The world will want to screw you – that's what happens in trade talks,” he said. “They have no interest in giving the UK a deal on trade”
4/11 Tim Martin
JD Wetherspoon's chairman has said claims that the UK would see serious economic consequences from a Brexit vote were "lurid" and wrong: “We were told it would be Armageddon from the OECD, from the IMF, David Cameron, the chancellor and President Obama who were predicting locusts in the fields and tidal waves in the North Sea"
5/11 Mark Carney
Governor of Bank of England is 'serene' about Bank of England's Brexit stance: “I am absolutely serene about the … judgments made both by the MPC and the FPC”
6/11 Christine Lagarde
IMF chief urges quick Brexit to reduce economic uncertainty: “We want to see clarity sooner rather than later because we think that a lack of clarity feeds uncertainty, which itself undermines investment appetites and decision making”
7/11 Inga Beale
Lloyd’s chief executive says Brexit is a major issue: "Clearly the UK's referendum on its EU membership is a major issue for us to deal with and we are now focusing our attention on having in place the plans that will ensure Lloyd's continues trading across Europe”
8/11 Colm Kelleher
President of US bank Morgan Stanley says City of London ‘will suffer’ as result of the EU referendum: “I do believe, and I said prior to the referendum, that the City of London will suffer as result of Brexit. The issue is how much”
9/11 Richard Branson
Virgin founder believes we've lost a THIRD of our value because of Brexit and cancelled a deal worth 3,000 jobs: We're not any worse than anybody else, but I suspect we've lost a third of our value which is dreadful for people in the workplace.' He continued: "We were about to do a very big deal, we cancelled that deal, that would have involved 3,000 jobs, and that’s happening all over the country"
10/11 Barack Obama
US President believes Britain was wrong to vote to leave the EU: "It is absolutely true that I believed pre-Brexit vote and continue to believe post-Brexit vote that the world benefited enormously from the United Kingdom's participation in the EU. We are fully supportive of a process that is as little disruptive as possible so that people around the world can continue to benefit from economic growth"
11/11 Kristin Forbes
American economist and an external member of the Monetary Policy Committee of the Bank of England argues that the economy had been “less stormy than many expected” following the shock referendum result: “For now…the economy is experiencing some chop, but no tsunami. The adverse winds could quickly pick up – and merit a stronger policy response. But recently they have shifted to a more favourable direction”
"There were lots of moments in the referendum campaign but for me that was one when my jaw did hit the floor. Very frustratingly, the story did eventually emerge, whether it was true or not."Reuse content