Sir John Major has recalled the Queen's "radiant smile which lights up a room" following the news of her death.
The former Huntingdon MP and ex-prime minister told the BBC: "It is heartbreaking news.
"It’s news that one day we knew we would have, but we always hoped would be delayed and would be some way away.
"It is very hard to take it in that that radiant smile which lights up a room and lights up a country is just not going to be light for us anymore; it’s very hard to imagine.”
The Queen died at Balmoral on September 8.
While prime minister, Sir John reflected on meetings he had with the Queen, which did not always fit to schedule.
"The private meetings that the prime minister has with the Queen, which are perhaps scheduled for 45 minutes in my experience, never lasted remotely under an hour and often someway beyond it," he said.
"There was a great deal of amusement in them, there was a great deal of humour in them, there was a bit of gossip in them.
"And apart from the serious matters that were discussed, I think people would’ve been extraordinarily surprised if they realised the depth of information the Queen had about the lives of people in every conceivable part of the United Kingdom."
Sir John said the Queen was "extraordinarily well briefed", such as on foreign affairs.
"She would often say if there was a difficulty of a foreign leader, ‘well I met him many years ago’ or ‘I knew his father’," he said.
"There was always a wise word to be had, and those meetings with the Queen were one of the better parts of a Prime Minister's week."
The nation has entered a period of national mourning following the Queen's death at the age of 96.
The news of her death was announced in a statement on behalf of the Royal Family just after 6.30pm on Thursday, September 8.
The statement read: “The Queen died peacefully at Balmoral this afternoon.
"The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow.”
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