London (CNN) From the moment Boris Johnson joined the race to be Britain's next prime minister last month, victory has seemed likely for the larger-than-life Conservative politician.

The former foreign secretary and London mayor's grandiose character was always going to be a central part of his campaign to replace the comparatively wooden Theresa May.

Now the line between Johnson's persona -- the most potent weapon in his political career -- and his private life has become murky.

Johnson has repeatedly dodged questioning over what happened in Friday's early hours, when police were called to an alleged altercation at the south London home he shares with girlfriend Carrie Symonds.

The incident has raised serious questions, not just over Johnson's character, but at what point a future prime minister's private life becomes off-limits to the public.

This is far from the first time Johnson's personal life has made headlines. Reports of his alleged extra-marital affairs have long graced the pages of the UK tabloids. In 2004 he was fired as a spokesman on cultural affairs for the Conservative party after revelations about his private life.

Johnson has four children with his second wife, Marina Wheeler. The couple separated last year.

But last week Johnson supporter and fellow Conservative MP Johnny Mercer was left floundering after a BBC journalist put him on the spot about how many children Johnson has fathered.

"What Boris chooses to do in his personal life and what he chooses to talk about is entirely a matter for him," Mercer said. "It would be entirely inappropriate for me to talk about any of that."

Johnson has never publicly addressed the issue of extra-marital children. CNN has contacted Johnson's office for comment but had not received a reply at time of publication.

In a BBC interview late on Monday, Johnson continued to shutdown any media discussion of the incident with Symonds.

"I do not talk about stuff involving my family, my loved ones," he said. "And there's a very good reason for that. That is that, if you do, you drag them into things that really is ... not fair on them."

When the private becomes public

Politicians "don't forfeit their right to privacy simply because they run for office," according to Jeffrey Howard , a lecturer in political theory at University College London. But the nature of Friday's incident -- an alleged domestic row involving police -- is in the public interest and deserves an explanation, he said.

In a recording made by neighbor Tom Penn, Symonds is heard telling Johnson to "get off me" and "get out of my flat," the Guardian newspaper reported.

Penn said he knocked on the door, got no response, then called police. In turn, London's Metropolitan Police said in a statement that officers arrived and "spoke to all occupants of the address, who were all safe and well."

There is no suggestion that Johnson's behavior in this instance amounted to abuse. But Johnson nevertheless "owes the public just an explanation of what happened, so there isn't even the appearance of anything morally amiss," Howard said.

John Griffin, a major Conservative party donor, seems to agree. "We deserve an explanation about that row, and he has to handle it properly," Griffin told The Guardian on Monday. "He can't assume that we are going to support him when he has not explained every detail."

Trial by media?

Johnson sees things differently. At a hustings event in Birmingham over the weekend, moderator Iain Dale asked the politician at least four times about the incident -- which Johnson each time avoided, instead saying that people did not "want to hear" about the reported row.

In any case, the British media certainly want to speculate on it.

On Monday, George Osborne, former Conservative chancellor and now editor of London paper the Evening Standard, tweeted an image of the newspaper's front page showing Johnson and Symonds together.

The image shows the pair holding hands and gazing into each other's eyes reportedly in the Sussex countryside.

The Evening Standard reported that a source from Johnson's campaign confirmed that the picture was genuine, but couldn't say who took the photo or whether the pair knew that it was being taken.

Speculation was rife on social media that the photo was either old or staged.

Today's ⁦@EveningStandard⁩ as a picture of the happy couple emerges pic.twitter.com/Yjxa99Ng9B — George Osborne (@George_Osborne) June 24, 2019

Johnson is a key Brexiteer and over the weekend some of Britain's tabloid newspapers attempted to frame Friday's incident as an attack by Remain-voting neighbor Penn and his wife.

The Sun described the couple as 'left-wing playwrights," while the Daily Mail reported it had seen anti-Conservative tweets on her Twitter account, which has now been deleted.

In response, Penn said his actions were in the public interest, and that the "attempts from some areas of the press to instead focus their stories on us, and in particular my wife, have been eye-opening, and very alarming."

"I would encourage anyone to record any instances where they feel concerned for another person's safety," he added.

Whether the front-runner to be prime minister owes the public an explanation of his messy love life is up for debate.

"I'm generally skeptical of the idea that there's a deep distinction between people's private moral character and their public moral character," said Howard. "I think there's simply moral character."

He added that when the "alleged character defect speaks to an issue of significant public interest, then I think it's important for us to hear more."