Early on Thursday morning, Australian man Alek Sigley — who had unexpectedly disappeared a week earlier in North Korea — was released from detention, landing safely in China.

Key points: Sweden was the first Western country to establish an embassy in North Korea, back in 1975

Sweden was the first Western country to establish an embassy in North Korea, back in 1975 Sweden has a policy of remaining politically neutral and with as many countries as possible

Sweden has a policy of remaining politically neutral and with as many countries as possible An expert said it would have been "almost impossible" for Australia to achieve the release of Alek Sigley without the help of Sweden

Mr Sigley, 29, had been studying for a masters degree in Korean literature at Kim Il-sung University in Pyongyang, when he was reported missing in late June.

It was not known whether he had been arrested, placed in detention or worse.

After Mr Sigley arrived in Beijing, accompanied by Swedish Government envoy Kent Rolf Magnus Harstedt, he boarded a flight to Japan, the home country of his wife, Yuka Morinaga, which arrived at 10:14pm local time.

With a smile, Mr Sigley strolled through the arrivals area at Tokyo's Haneda airport.

But he was not interested in shedding any more light on why he was detained in North Korea. He did not answer questions from reporters.

Escorted by the Australian embassy's consul general, Mr Sigley went through immigration and out a special exit away from more waiting media.

It may surprise many that it was the behind-the-scenes work from Sweden that helped secure Mr Sigley's safe release, with Prime Minister Scott Morrison expressing his "deepest gratitude to the Swedish authorities for their invaluable assistance".

It was not the first time Sweden acted as a 'middle man' between other Western countries and the secretive communist state.

Why Sweden?

The Scandinavian country has a unique relationship with North Korea, which has been largely shunned by the international community because of its widespread human rights abuses and weapons program.

Sweden was the first Western country to establish an embassy in North Korea, back in 1975, with the prospect of trade being one of the biggest influencers for these initial ties; Swedish companies such as Volvo, Atlas Copco and Kockums were keen to begin exporting to the Asian country.

The export strategy didn't play out — the 1,000 Volvos that North Korea ordered several decades ago have never been paid for — but it opened diplomatic relations.

Sweden is also one of the biggest providers of international aid, providing about AU$6.1 million every year to the "hermit kingdom".

Until 2001, when Germany joined, Sweden was the only Western embassy in North Korea, and it is still only one of 25 in the country. The Swedish embassy also represents Australia, Canada and the US.

Over the years, Sweden has garnered a reputation as a neutral player and its embassy and diplomats have played a crucial role in helping other countries retrieve their citizens from the clutches of North Korea.

In 2017, Swedish officials helped with the return of US student Otto Warmbier, who was jailed in North Korea amid claims that he stole a propaganda poster.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 59 seconds 59 s Mr Sigley's release was announced by Mr Morrison during Question Time.

After 17 months in detention, he was flown back to his home state of Ohio in a coma and showing signs of being tortured; he never regained consciousness and died several days later.

Professor Joseph A Camilleri, an expert in international relations at La Trobe University, told the ABC that it would have been "very unlikely" that Mr Sigley would have been released without Sweden's help.

"It wasn't too long ago that Australia did have diplomatic relations with North Korea but we chose to break them because of disagreements over the country's conduct. It was a silly thing to do," he said.

Only China and Russia have stronger relations with North Korea than Sweden, Professor Camilleri said.

Australian Alek Sigley was surrounded by media in a Beijing airport after being released. ( AP )

'It works both ways'

The friendly relations between the two countries has been demonstrated multiple times.

Sweden made history when then-Prime Minister Göran Persson visited North Korea in 2001 — the first western leader to do so — as the head of a European Union delegation for talks on increasing diplomatic ties.

In 2018, that visit was reciprocated when North Korea's deputy foreign minister visited Sweden to discuss the country's summit with the US later that year.

There were talks for some time that Sweden would host the historic summit, which was later held in Singapore.

Professor Camilleri said that this demonstrates that Sweden is not just of assistance to countries, such as Australia, who have no diplomatic representation in North Korea.

"North Korea can also take advantage of Sweden's neutral position to get certain things done that they overwise wouldn't be able to do, so it works both ways.

"And of course it suits Sweden to keep demonstrating its credentials on the diplomatic landscape."

Did Donald Trump do anything?

There is speculation that US President Donald Trump's recent meeting with the North Korean leader may have played a role in the release of Mr Sigley.

Mr Trump made history when he became the first US president to set foot inside North Korea when he met Kim Jong-un Kim at the demilitarised zone (DMZ) on the border of North and South Korea on June 30.

Professor Camilleri said it was possible that Mr Trump advocated for Mr Sigley's release, although the normally chatty US leader has not said anything.

Last month, Donald Trump became the first US President to set foot inside North Korea. ( Reuters: Kevin Lamarque )

The June 30 meeting, which followed the G20 Summit, was the third time the two leaders have met.

The thawing of relations between the two foes is a sign that Australia should follow suit and re-establish direct diplomatic ties with North Korea, Professor Camilleri suggested.

"[If] you don't have a direct, separate avenue for making your own judgements, let alone taking any initiatives that may be in your favour, you're placing yourself at a disadvantage."

The big question — why?

While the release of Mr Sigley was undoubtedly a success, it remains a mystery why he was taken into detention in the first place.

Upon landing in Beijing, Mr Sigley would not answer questions about why he was detained or his treatment, only saying "I'm fine, I'm very good".

Australian Alek Sigley married his Japanese-born wife Yuka Morinaga last year in Pyongyang. ( Facebook: Alek Sigley )

Professor Camilleri said only Mr Sigley could provide those answers, but it might not be in his best interests to do so.

Along with his studies, Mr Sigley is the founder of Tongil Tours, an Australian-based company specialising in guided tours to North Korea.

"I would not be surprised if he did not [speak out] because his business is based in North Korea and he would want, presumably, to continue with the tourist enterprise and he seems well placed to do so."