Jeremy Corbyn is set to join Sadiq Khan to celebrate a potentially stunning victory for Labour in the London Mayoral race.
HuffPost UK understands that the Labour leader intends to be fully involved to mark what would be a huge boost to party morale if Khan defeats his opponent Zac Goldsmith.
Live election results put Khan ahead by 9% on first preference votes, in line with most of the polls that suggested he would win with a comfortable margin once second preferences were taken into account.
Some figures within Labour had suggested earlier this week that Khan was so determined to distance himself from Corbyn that he would refuse to appear alongside him in the victory celebrations.
But Corbyn allies have told HuffPost UK that idea is "ridiculous", with one friend saying "try and stop him" from turning up to City Hall. An alternative is for a joint event at Labour HQ.
Taking London from the Tories after the eight-year reign of Boris Johnson is seen as a massive coup for the party leadership.
When Boris won his first London Mayoral victory in 2008, he went straight to Tory party HQ to celebrate alongside David Cameron to mark a huge coup for the party as a whole.
Khan nominated Corbyn for the party leadership last summer but although he has said he does not "regret" doing so, he did not vote for him in the contest and sharp tensions have emerged between some of their supporters.
The Labour mayoral candidate has spent most of his campaign distancing himself from the leader, on everything from their approach to business to prioritising London transport infrastructure.
Khan leaflets were different from Labour's national local elections campaign, and didn't use the 'Elections Are About Taking Sides' slogan used by the party across the country.
His team have also had to contend with the Tory charge that a Khan win would be a victory for the 'Corbyn experiment' in London.
No one in Labour wants to pre-empt the result, but it is understood that at the very least, Khan will have to agree to a photocall with his party leader on Saturday if he wins.
Another key factor is that Corbyn is a London MP and has long had supporters within the London Labour Party.
However, some suggest that Corbyn will turn up to City Hall tonight to mark the victory.
Another option is for Khan to turn up to Labour HQ to be greeted by Corbyn and party staffers.
The pair of appeared together rarely on the campaign trail, including once when during a minimum wage event outside Arsenal football club, where they were photographed wearing red and white scarves.
But during the 'short campaign' they appeared together on Easter Saturday, when the media were focused elsewhere and London's Evening Standard didn't publish for another three days.
Corbyn turned up to a Khan 'phone bank' last week, but the Mayoral candidate was not present, prompting MPs to believe he felt any photos with the leader would undermine the final days of his campaign.
Khan has repeatedly insisted that the race is "not a referendum" on Corbyn's leadership and is more about his own vision for the capital.
Yet Corbyn supporters point out the leader has hit back hard to defend Khan from David Cameron's 'extremism smears' and some believe Corbyn has a right to partially 'own' the victory for the whole Labour party.
And many trade union activists believe that Khan owed his victory over Tessa Jowell in the Labour selection to the perception that he was the 'Corbyn' candidate.