"Vote Blair, Get Brown!" It was meant to be a vote-winning slogan for Britain's opposition Conservatives - showing that a win for Prime Minister Tony Blair at today's poll would likely foreshadow a future handover to his finance minister Gordon Brown.
But the ad was quickly abandoned when the Conservatives realised that instead of bristling at the prospect of not getting the man they vote for, many Britons were delighted.
Tainted by Iraq and eight years into the job, Mr Blair is past his sell-by date for some. Polls predict that will hurt his parliamentary majority today but not prevent victory.
Mr Brown's political capital, on the other hand, has never been higher. His high-profile intervention is widely deemed to have "saved" the campaign, polls show him more popular than his boss, and the government's trump card, the economy, is his baby.
"Mr Brown has been the dominant character in this election ... Blair hugs him as closely as Linus does his blanket in Peanuts," columnist Matthew d'Ancona said.
The powerful pair's unexpected inseparability has been a crucial feature of the campaign.
From tomorrow, assuming no upset, the when, if and how of a Blair-Brown transition looks set to dominate UK politics.
Mr Blair has said he would step down after serving a full third term and that Mr Brown "will make an excellent prime minister".
But many think Mr Blair's announcement of political mortality will make him a lame-duck leader and expect him to step down earlier. Losing a planned 2006 referendum on the EU treaty - that most Britons oppose - may precipitate that.
"Blair will step down in one year if the euro referendum fails and in 2-3 years if not," said Patrick Dunleavy at the London School of Economics. "Labour party telesales people are already collecting comments on Gordon Brown as Prime Minister."
The incongruous alliance between Blair, 51, an Oxford-educated lawyer, and Mr Brown, 54, the gruff-speaking son of a Scottish clergyman, has been one of the most powerful and fascinating political partnerships in British history.
As young opposition legislators, they shared a cramped office together. Then, according to political folklore, they struck a deal in 1994 for Mr Blair to take the Labour leadership but hand over to Mr Brown in a second term once they won power.
After sweeping into office in 1997, tension between the pair has never ceased, according to insiders and aides for both who tell of blazing rows over both policies and power.
Tensions between the two were nicknamed the "TB-GBs". Once, according to a Mr Blair biographer, Mr Brown thumped the table and yelled at his boss: "When are you going? I want the job now!"
Despite such history, it has all been sweetness and light on the campaign trail as - whether cosmetically or for good - the pair have successfully buried their differences in public.
Private Labour polling showed images of Mr Blair alone brought a hostile response from voters and images of Mr Brown moderate warmth, but together they inspired greater enthusiasm.
So sticking together like limpets, they have starred in a sickly-sweet TV ad, exchanged praise ad nauseam, nodded in agreement on policy and shared endless photo opportunities.
Even on Iraq, with Mr Blair's ratings battered over support of the US-led invasion, Brown has eschewed the chance to mark a difference and said he would have acted the same.
In return, Mr Blair has virtually guaranteed Mr Brown will remain Chancellor of the Exchequer in a Cabinet reshuffle expected tomorrow if he wins. That was a far cry from speculation a month ago that Mr Blair would demote his rival after the election.
"Instead, Mr Brown has been Mr Blair's essential prop, promised in return both an extension of his lease on the chancellorship and Mr Blair's endorsement for the succession to 10 Downing Street," Mr Blair biographer Philip Stephens said.
"The fact this is Mr Blair's last election has lifted the burden of uncertainty from Mr Brown. Whether or not the prime minister has broken previous promises to stand down, by his own admission his tenancy of 10 Downing Street is now finite."
If Mr Blair dared change his mind, Mr Brown still has what media dub "the nuclear option" of a straight leadership challenge.
Mr Brown is dearly loved in the Labour rank-and-file who see him as more in touch with the party's socialist roots than Mr Blair, the man who changed its name to New Labour.
A Brown premiership would be unlikely to break radically with Mr Blair policies, but may be more cautious towards Europe and row back on some private funding of public services.
Other potential candidates for the Labour leadership, such as Health Secretary John Reid or Home Secretary Charles Clarke, would have their work cut out beating Mr Brown. As one seasoned political writer concluded this week: "The transition to Gordon Brown is under way."