Thailand is set to crown a new monarch this month after King Bhumibol Adulyadej’s death ended his 70-year reign – but the former ruler’s only son and heir, Crown Prince Maha Vajiralongkorn, is not popular with everyone.

In fact he is known more for his eclectic dress sense, scandal-plagued past and failed marriages than any regal qualities.

The 64-year-old Crown Prince was pictured at Munich airport earlier this year wearing a small white crop-top, faded slim-fit jeans and a fake tattoo sleeve.

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And he has already asked to delay becoming king, raising fears of deepening instability in Thailand after the death of his much-loved father.

Who is the king-in-waiting?

Born in 1952 in Bangkok’s Royal Palace, Prince Maha was educated in the UK at King’s Mead School and Millfield School before attending Australia’s Royal Military College. He spent much of his working life training with armed forces in Britain and the US, winning an array of military titles and a pilot’s license after developing a love of aviation.

He rushed home from Germany – where he spends much of his time, reportedly with a former Thai Airways air hostess who he is planning to marry – when his father’s health deteriorated and has since requested to delay taking to the throne so, he says, he has more time to mourn.

Experts believe this could deepen a period of instability in Thailand that has included two coups, anti-government protests and a bloody fight for secession by Muslim separatists in the country’s southern provinces.

The crown prince is seen to lack the public popularity that gave his father's rule legitimacy, raising fears of a power struggle in the south-east Asian country.

Crown Prince Maha Vajiralongkorn (left) photographed at Munich airport in July 2016 (Bild)

Why is he so controversial?

It is Prince Maha’s “playboy” personal life that has attracted most attention. He is famous for his dedication to his pet poodle, Foo Foo, which was awarded the rank of Air Chief Marshal in the Royal Thai Air Force and given its own Wikipedia page.

It has frequently appeared at official functions; including accompanying the Crown Prince to a 2007 reception hosted in his honour by the US Ambassador Ralph Boyce.

Mr Boyce allegedly recounted the event in a leaked cable, writing: “Foo Foo was present at the event, dressed in formal evening attire complete with paw mitts, and at one point during the band’s second number, he jumped up on to the head table and began lapping from the guests’ water glasses, including my own.

“The Air Chief Marshal’s antics drew the full attention of the 600-plus audience members, and remains the talk of the town to this day.”

When the dog died last year, it was given a four-day funeral complete with Buddhist rites before being cremated in an extravagant ceremony.

Foo Foo and its owner hit the headlines in 2014 when opponents of the Crown Prince leaked a video showing his third wife, Princess Srirasm, lying on the floor feeding the dog cake while wearing nothing but a G-string.

The footage prompted a national scandal in Thailand and attracted news coverage across the world.

How do people feel about him becoming king?

The leaking of the tape marked the eruption of below-the-surface tensions among the country’s elite as to who should succeed King Bhumibol.

Some would prefer the Crown Prince’s younger sister, Princess Maha Chakri Sirindhorn, to take the throne but Thai law forbids a female monarch.

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A diplomatic cable from 2010, released by Wikileaks, reported members of Thailand’s political elite expressing hopes that the King would override the laws in order to appoint the Princess as his heir.

They highlighted Prince Maha’s alleged record of meddling in politics and “embarrassing financial transactions”. The cable records officials saying the Crown Prince “could not stop either, nor would he be able, at age 57, to rectify his behaviour”.

What about his family?

Prince Maha has been married three times. His first – to his cousin – reportedly included him fathering five children with a mistress, who he then married instead.

The second wife left the country when the relationship ended.

Thai King Bhumibol Adulyadej - Life in Pictures Show all 10 1 /10 Thai King Bhumibol Adulyadej - Life in Pictures Thai King Bhumibol Adulyadej - Life in Pictures Royal guards shade Queen Elizabeth II and Thai King Bhumibol Adulyadej from the sun with traditional Thai parasols during the welcoming ceremony at Bangkok military airport Reuters Thai King Bhumibol Adulyadej - Life in Pictures The Thai royal family, King Bhumibol Adulyadej, Crown Prince Maha Vajiralongkorn & Queen Sirikit Getty Thai King Bhumibol Adulyadej - Life in Pictures Thai King Bhumibol Adulyadej reviews royal guards at a ceremony marking his 69th birthday Getty Thai King Bhumibol Adulyadej - Life in Pictures Thai King Bhumibol Adulyadej takes pictures during the royal ploughing ceremony in Bangkok Getty Thai King Bhumibol Adulyadej - Life in Pictures Thai King Bhumibol Adulyadej, the world's longest serving monarch, and Queen Sirikit preside over a ceremony marking the 50th anniversary of the king's accession to the throne Getty Thai King Bhumibol Adulyadej - Life in Pictures King Bhumibol Adulyadej of Thailand rides with French President de Gaulle in French official Citroen convertible upon his arrival at Orly airport, south of Paris Getty Thai King Bhumibol Adulyadej - Life in Pictures King Bhumibol Adulyadej of Thailand rides down the Champs-Elysees with French President de Gaulle Thai King Bhumibol Adulyadej - Life in Pictures Thai King Bhumibol Adulyadej and Queen Sirikit stand near Belgian King Baudouin I, during their official visit to Belgium Getty Thai King Bhumibol Adulyadej - Life in Pictures King Bhumibol Adulyadej of Thailand on a stopover at the Touquet airport on August 1948 during his journey to Great Britain Getty Thai King Bhumibol Adulyadej - Life in Pictures French President de Gaulle and his wife alongside King Bhumibol Adulyadej of Thailand and his wife attend a show at the Opera de Paris Getty

In 2011 four of the children she had with the Crown Prince published a letter claiming they had been abandoned by their father and banned from returning to Thailand.

They wrote: “We were ordered by our father not to return home to Thailand ... We were afraid to risk even demonstrating the slightest inference of disrespect toward the Royal Family.”

Prince Maha ended his relationship with his third wife, Princess Srirasm, in December. Her parents were later thrown in prison for two-and-a-half years for “royal defamation”.

Who will his allies and enemies be?

The fears about his ascension to power go deeper than concerns about his romantic life and canine commitment.

The Crown Prince is known to be friends with former prime minister Thaksin Shinawatra, the businessman and former owner of Manchester City, who was ousted as the Thai premier in 2006.

Fears of a potentially powerful partnership between Mr Shinawatra and the future king were reported to have been the motivation in part for military coups in 2006 and 2014.

Former Thai prime minister Thaksin Shinawatra was outed in a 2006 coup after public protests (AFP/Getty Images)

Amid the turmoil, prominent members of Thailand’s ruling class have reportedly been killed in a sign of what could become a more widespread conflict.