Ken Livingstone's youngest secret lovechild is a fifteen-year-old boy and he has two grown-up daughters as well

In a further development after a week of revelations, it appears that two of his partners conceived just a short time apart.

Mr Livingstone has stated he is "an involved father" with all of his secret children, which includes a 15-year-old boy as well as two teenage girls.

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The story of Mr Livingstone's tangled love life started in 1982 when he began relationship with Kate Allen, UK director of Amnesty International.

But during the early 1990s Livingstone, who was then Labour MP for Brent, started seeing, Janet Woolf a local Labour party activist.

She then gave birth to his son, who is going to be 16 this year.

During that period Mr Livingstone found the energy to start a relationship with a third lover who gave birth to his two daughters.

One of the girls was born around the same time as the son in the early 1990s, while the other daughter was born two years earlier.

In the final chapter of his love life, which he has always be open about, his relationship with Ms Allen ended and he found a new partner, his office manger, Emma Beale.

The couple now have two children, Thomas, five, and Mia, four. All five children of the Mayor's children are thought to regularly spend time with each other, including going on holiday in Sardinia and Greece with him.

Mr Livingstone has always been very guarded about his secret children.

After the birth of his first child with his current partner, Ms Beal, in 2002, Mr Livingstone made no move to correct the widespread report that it was his first child.

While Londoners believed this to be the case - and congratulated the mayor on becoming a father for the first time at the age of 57 - close friends knew the truth.

They also knew that Mr Livingstone was extremely touchy about his two secret families.

"This has always been a big no-no with Ken," one said. "You just don't go there."

But now he has revealed the existence of his three unknown children, apparently because the fact was about to be published in a new biography.

It seems he would have preferred to keep the existence of his three unknown children a secret, but he was asked about them by Andrew Hosken, the BBC journalist and author whose new biography of the mayor is due out soon.

Hosken told the "During one of my meetings with Ken at City Hall I raised the question of the children."

Mr Livingstone sought to shrug off the issue with a return to the mayoral campaign trail today.

Less than four weeks from the May 1 election, he is fighting for his political life after polls showed him behind Mr Johnson in the race for Mayor.

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Critics immediately suspected that the latest revelations about Mr Livingstone's family were a calculated attempt to pre-empt newspaper exposes and prevent any further damage to his re-election bid.

A new biography containing details of his family life - "Ken: the Ups and Downs of Ken Livingstone" by Mr Hosken - is set to be serialised imminently, but Mr Livingstone's office categorically denied claims that it had deliberately leaked the news.

When asked if any member of his campaign team had leaked the story, his spokeswoman said: "Absolutely not."

Mr Livingstone launched a passionate defence of his right to keep his family life private.

He told the BBC: "I don't think anybody in this city is shocked about what consenting adults do.

The London Mayor has been an advocate of the importance of "good parenting".

At a mayoral debate on Monday, he claimed that the many children descended into violence because they lacked a proper "father figure".

He has also claimed that parents are failing to install a proper "moral code" into their children.

But Mr Livingstone rejected charges of hypocrisy, claiming that there was "no problem at all" for his political views as a result of his private affairs.

He insisted that Ms Beal had known about his other children.

"There is nothing in my private life that is not known to my partner, family or my close friends.

"I'm quite happy with my private life and the people who have shared my private life over the last 40 years.

"I don't see any complaints. No one has ever found anything in my private life that was illegal or immoral."

In a statement, Mr Livingstone's campaign referred to the fact that both his Tory and Liberal Democrat rivals had had issues in their private lives in the past.

Mr Johnson's extra-marital affair with a journalist was exposed by the News of the World four years ago, while Mr Paddick was smeared by a former partner who made false claims about their life together.