Thai King Bhumibol Adulyadej
Thai King Bhumibol Adulyadej reads a statement convening Parliament in front of 391 newly elected members of parliament at Ananta Samakhom throne in Bangkok on July 10Reuters

Thailand's King Bhumibol Adulyadej, the world's longest-reigning monarch, passed away on Thursday. The royal palace confirmed the news that King Bhumibol, the ninth king of the 234-year-old Chakri dynasty, died aged 88, but the palace has not divulged any information on the mourning or succession.

"His Majesty has passed away at Siriraj Hospital peacefully," the palace said in a statement, adding that he died at 3.52 pm (8.52 am GMT).

On Sunday, the royal palace had announced that the 88-year-old king was in unstable condition and was put on the ventilator, triggering an outpouring of grief. Hundreds of people in Thailand had gathered outside Siriraj Hospital wearing the auspicious colour, pink, to pray for the king's health.

Following the news, the nation has plunged into mourning. Several social media users changed their profile pictures that had a message "love the king." As soon the news of his death spread, the country's stock market and currency also tumbled. Prime Minister Prayut Chan-o-cha also cancelled his overseas trip.

Now, speculations about the next Thailand's king have started making the rounds. There are reports that his heir, 64-year-old Crown Prince Maha Vajiralongkorn, will ascend to the throne. However, an official announcement is yet to be made.

Meanwhile, scroll down to take a look at some of the rare and unseen photos of King Bhumibol Adulyadej.

Thai King Bhumibol Adulyadej
US President Bill Clinton (L) meets King Bhumibol Adulyadej in the royal residence November 26. Clinton arrived in Thailand for a brief state visit to commemorate the Thai king's 50th birthday on the throne and to help boost commercial ties.Reuters
Thai King Bhumibol Adulyadej
French President Jacques Chirac (L) bows as he is greeted by King of Thailand Bhumibol Adulyadej and Queen Sirikit at the Ananta Samakhom Throne hall as the twenty five leaders and senior officals (some with their wives) arrive for an audience during the Asia Europe Summit meeting (ASEM) March 1. ASEM brings together twenty-five Asian and European nations and is aimed at paving the way for new economic and strategic relationships between the two regionsReuters
Thai King Bhumibol Adulyadej
Royal guards shade Queen Elizabeth II (L) and Thai King Bhumibol Adulyadej (R) from the sun with traditional Thai parasols during the welcoming ceremony at Bangkok military airport on October 28. The Queen and The Duke of Edinburgh are in Thailand on a five-day visit to commemorate the 50th anniversary of Thai King's accession to the throne.Reuters
Thai King Bhumibol Adulyadej
Britain's Queen Elizabeth II smiles as she greets Thailand's Queen Sirikit as the King Bhumibol Adulyadej looks on at a reception at the British Ambassador's residence in central Bangkok October 30.Reuters
Thai King Bhumibol Adulyadej
Thailand King Bhumibol Adulyadej sits on the Royal Barge during the Royal Barge Procession on the Chao Phraya River in Bangkok November 4. More than 2,000 rowers sent a procession of glittering royal barges gliding down Bangkok's River of Kings in the most spectacular celebration of constitutional monarch King Bhumibol Adulyadej's 72nd year.Reuters
Thai King Bhumibol Adulyadej
Thai King Bhumibol Adulyadej is accompanied by Queen Sirikit as they review an honour guard during the trooping of the colour ceremony for the King's birthday in Bangkok December 3. The Thai monarch will turn 70 December 5.Reuters
Thai King Bhumibol Adulyadej
Denmark's Queen Margrethe II (R), escorted by Thailand's King Bhumibol Adulyadej, reviews a royal military guard of honour upon her arrival in Bangkok February 7, 2001. Queen Margrethe II is on a six-day visit to Thailand at the invitation of Thailand's royal family.Reuters
Thai King Bhumibol Adulyadej
Argentine President Carlos Saul Menem (L) shakes hands with Thai King Bhumibol Adulyadej at Chitrlada Palace in Bangkok, February 18. Menem arrived in Thailand for a three-day visit to seek stronger trade and bilateral ties. Menem, who flew from Vietnam, is the second Argentinian leader to visit Thailand since 1961.Reuters