Boris Johnson and Rishi Sunak have held talks as they edge closer to the deadline for nominations in the contest to replace Liz Truss as prime minister.
Two separate sources told the BBC the meeting took place, but neither camp has disclosed what they discussed.
Rishi Sunak continues to forge ahead in the race, gathering the support of 128 MPs from all wings of his party, including former Johnson allies.
Mr Johnson is in second place with 53 backers, according to the BBC's tally.
However his campaign claims he has the support of 100 MPs – the number required to officially enter the race.
Mr Sunak's supporters raised doubts over this and called for the former PM to show proof.
Penny Mordaunt is the only candidate to officially declare they are in the race, but she lags behind on support with 23 MPs.
The BBC has been keeping a running total of MPs who have gone on the record with support.
The voting intentions of only 204 out of 357 Conservative MPs are currently known and have been verified by the BBC, leaving many still to declare their interest.
The hopefuls have until 14:00 BST on Monday to get enough support to run, qualifying them for the next stage of the race.
If the party's MPs get behind just one candidate, we could have a new prime minister by Monday afternoon.
But if not, it will then go to an online ballot of the Conservative party membership, with the result to be announced on Friday.
Polling suggests Mr Johnson, who has returned from a Caribbean holiday to consider his options, would be favourite to win a members' vote.
Throughout Saturday, MPs were publicly declaring support for their favoured candidate.
Mr Sunak picked up backing from all wings of his party, including the right, and from figures like Mr Johnson's former Chief of Staff Steve Barclay, his former Brexit Minister Lord Frost, Kemi Badenoch, the International Trade Secretary and Northern Ireland Minister Steve Baker.
Mr Baker – an influential MP on the right of the party – said Mr Johnson would be a "guaranteed disaster", and specifically expressed concern about an ongoing parliamentary investigation into whether the ex-prime minister lied to Parliament over Covid rule-breaking.
He told Sky News a large number of Conservative MPs would "refuse to lay down their integrity" in order to defend Mr Johnson on the issue.
Ms Badenoch, who made a big impact in the last Tory leadership contest but has ruled herself out this time, said in the Sunday Times that Mr Sunak was "the serious, honest leader we need".
Mr Sunak, who has yet to officially declare he is standing, also has the support of former chancellor and health secretary Sajid Javid, Security Minister Tom Tugendhat, former deputy prime minister Dominic Raab.
Pointing to the parliamentary probe facing Mr Johnson, Mr Raab told the BBC: "We cannot go backwards. We cannot have another episode of the Groundhog Day, of the soap opera of Partygate".
He said he was very confident Mr Sunak would stand, adding: "I think the critical issue here is going to be the economy. Rishi had the right plan in the summer and I think it is the right plan now."
The former PM has so far won the support of six Cabinet ministers: Ben Wallace, Jacob Rees-Mogg, Simon Clarke, Chris Heaton-Harris, Alok Sharma and Anne-Marie Trevelyan.
Also among supporters of Boris Johnson is former home secretary Priti Patel who said he could bring together a united team and lead the UK to a stronger and more prosperous future.
An ally of former home secretary Suella Braverman told the PA news agency she had been "heavily courted" by both Mr Johnson and Mr Sunak and was likely to decide who to back on Sunday.
Meanwhile, Andrea Leadsom, former business secretary, said Ms Mordaunt was the unifying candidate; an experienced minister and a "robust Brexiteer".
Writing in the Express on Sunday, Ms Mordaunt set out her plan to "unite the party and the country" and said the Tories had "let ourselves become distracted by internal disputes".
She stressed the need to "make Brexit work", "focus on the potential of all our citizens" and "defend our Union and its territorial integrity".
Conservative MP Bob Seely said "I think we owe the country a collective responsibility to apologise" and said he believes Ms Mordaunt has the best chance of providing "unity and leadership" within the party.
Mr Johnson's potential bid to return to power comes just seven weeks after his final day in No 10.
His successor, Liz Truss, is the UK's shortest-serving prime minister, stepping down after 45 days in power.
She announced her resignation on Thursday, after a series of humiliating U-turns forced on her by an adverse reaction to her tax policies in the financial markets.
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