Image copyright AFP Image caption Pregnant or not?

The sister of North Korean leader Kim Jong-un told officials in the South that she was pregnant during a recent visit to the Winter Olympics, South Korean media report.

There has been no confirmation from the South of Kim Yo-jong's reported comments, which are attributed to unnamed government sources.

But the intense speculation highlights the fascination with the North's opaque power structures and whether or not Ms Kim is indeed expecting shows just how little is known about the North's ruling dynasty.

Nothing but gossip?

"They are like a royal family and so this story becoming news is unavoidable," Andray Abrahamian, Research Fellow at Pacific Forum CSIS, told the BBC.

"Yet while it is gossip, it's gossip about a very important person in a country that's very difficult to understand."

The speculation and secrecy around the matter is perfectly in keeping with what else we know - or rather don't know - about the Kim family and in particular their offspring.

In most cases it is South Korean intelligence that is cited as a source. But in the past another, surprising, source of information has been retired US basketball star Dennis Rodman.

Having travelled to North Korea several times on the invitation of Kim Jong-un, Rodman said in 2013 that he'd met Mr Kim's wife - as well as a daughter of the couple.

That was news to everyone.

There's speculation Mr Kim might have two more children but that is merely based on prolonged absences of his wife from public view.

Image copyright AFP/KCNA Image caption Little is known about Kim Jong-un and his wife

So why the secrecy around the North's first family?

The narrative built by the North's propaganda machine of the country's leaders as towering giants might suggest their children are equally celebrated and hence proudly presented to the nation.

The deification of the leader

Yet the very fact they are presented as mythological figures may be the reason why their everyday life with wife and children is kept out of the spotlight.

"The system is very much one of an absolute monarchy," Fyodor Tertitskiy of North Korea watchers NK News told the BBC. Therefore, "Kim Jong-un's family is treated as something very separate from normal people."

"The North's leaders are presented as legendary figures," Mr Abrahamian adds. "Information about them is withheld not just from us but also the North Korean people themselves."

State propaganda has created an almost divine aura around the country's three leaders Kim Il-sung, Kim Jong-il and Kim Jong-un to ensure the legitimacy to rule is safely transferred to the next generation, observers believe.

"There is in fact no need to announce the birth of a baby in a way a royal family might do because it's far too early to decide on the line of succession," Mr Abrahamian explains.

Kim Jong-un for instance is Kim Jong-il's third son. "So there is no point in infancy or even in youth picking winners in that family."

In the case of Kim Jong-un, he made his first publicised appearance only in September 2010, just over a year before his father's death in December 2011. It's thought he was not the favourite to take over from his father and was named successor only after his death.

A very exclusive bloodline

The family line is of utmost important to the North's power structures. The personality cult is even enshrined in the North's ideological system, as the Mount Paektu bloodline.

Yet it is only attributed to the immediate ruling family - the aura of divine leadership does not extend to brothers and sisters like Kim Yo-jong.

Image copyright AFP Image caption Kim Yo-jong is a close adviser but no heir to the throne

While they might be an important support to the dynasty's power structure, they are presented to the country as ordinary party members in whichever political role they fulfil.

"Mr Kim's sister does not occupy a particular special place in the mythologising propaganda for the regime," Mr Abrahamian explains.

It would therefore be very unlikely that any children of a sibling would inherit the country's leadership from their uncle.

If indeed she were to have a child, it's thought it would be her second. Once again, though, even the existence of a first child is based on speculation and hearsay.

Which is why some North Korea pundits are tired of the endless rumour mill.

"I do not understand why it is such a big deal," Professor Andrei Lankov, director of Korea Risk Group and professor at Kookmin University told the BBC.

"People have a pleasant and useful habit of having sex - and having babies."