Boris Johnson is the prince across the water and irritatingly for David Cameron that water is only the narrow width of the Thames between Westminster and City Hall.
But in Birmingham the prime minister does not even have the protective moat of the capital's river to separate him from his biggest rival within the Conservative Party.
The highlight of conference is supposed to be the speech from the leader, who in this case has the added weight of being prime minister.
However Cameron's address is not the main event this year. Talk inside the conference fortress, erected in England's second city, is not about whether tickets have been acquired to see Cameron speak on Wednesday, but whether there will be room for everyone on Monday evening for the "Olympotastic" victory rally with Boris.
Similarly, rather than being relegated the graveyard Sunday night slot in the main hall for his keynote speech, Boris has been given a prime-time platform slot on Tuesday.
Far from restricting his appearances, Boris has made sure he is a constant if not dominant presence, kicking off proceedings on Sunday night by refusing to rule out running for leader of the party.
Knowingly prodding the press and pleasing his many supporters, he told BBC Radio 5 Live that it was "unverifiable" whether Cameron was a better prime minister than he would be.
And as for whether he like to be prime minister after he is done with being London mayor?
"After four years are up, heaven knows. I will be an old man."
Cameron's crown is far from slipping. But it makes it much easier for a Tory leader to be toppled if there is an obvious, and popular, replacement.
A poll conducted by the grassroots Conservative Home website that is hosting the Boris rally on Monday night found that while 50% of Tory activists are satisfied with Cameron;s performance, 49% are dissatisfied.
The survey also found that Boris was the overwhelming favourite to succeed Cameron, with 37% of Tory members backing the mayor to take over should the Tories lose the 2015 election.
Heaven knows what the three-day Boris show has done for the mayor's ego, which he admitted to 5 Live was "already in a bad enough shape".
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