There is a new leader at the helm of Forbes magazine’s regal rich list, with King Bhumibol Adulyadej of Thailand, the world’s longest-reigning monarch, knocking the Sultan of Brunei off the top spot, the Times of London reported.

Forbes said that the 80-year-old king had a $35 billion fortune, with his estimated net worth increasing sevenfold during the past year because of the increased transparency of his holdings.

The Sultan of Brunei was one of only two royals to record a surprise fall in wealth, dropping to fourth in the list, despite huge rises in the price of oil and gas.

Forbes rates the fortune of Sultan Haji Hassanal Bolkiah, 62, at $20 billion, adding that Brunei’s oilfields were in danger of drying up. “The sultan, who inherited the riches of an unbroken 600-year-old Muslim dynasty, has had to cut back on his country’s oil production because of depleting reserves,” the magazine said.

King Mohammed VI of Morocco was the only other royal to record a decline in wealth, with his estimated worth, mainly in phosphate mining and agriculture, falling 25 per cent to $1.5 billion after the nation was hit by a drought, and economic growth slowed to 2 percent.

Overall, it was a good year for monarchies, Forbes said. “As a group, the world’s 15 richest royals have increased their total wealth to $131 billion, up from $95 billion last year.”

The magazine noted that because many of the royals inherited their wealth, share it with extended families, and often control it “in trust for their nation or territory,” none of those on its list would qualify for the magazine’s famous annual world billionaires ranking.

“Because of technical and idiosyncratic oddities in the exact relationship between individual and state wealth, these estimates are perforce a blend of art and science,” it added.

"While we have tracked the fortunes of a few high-profile royals, like the Queen of England and Sultan of Brunei, for years, this is only the second time we have published a definitive list of the richest royals," Forbes said.

"Monarchs of such countries as Spain and Japan failed to make the cut."

King Bhumibol, 80 years old and the world's longest-reigning monarch after six decades on the throne, is regarded as semi-divine by many Thais, Reuters reported.

Queen Elizabeth II, 82, has slipped one place down the global rich list of kings and queens. She now sits at 12th, with an estimated net worth of $295 million.

Following is Forbes' ranking of the world's richest royals:

1. King Bhumibol Adulyadej (Thailand)

2. Sheikh Khalifa bin Zayed al-Nahayan (United Arab Emirates)

3. King Abdullah (Saudi Arabia)

4. Sultan Hassanal Bolkiah (Brunei)

5. Sheikh Mohammed Bin Rashid al-Maktoum (Dubai)

6. Prince Hans Adam II (Liechtenstein)

7. Sheikh Hamad bin Khalifa al-Thani (Qatar)

8. King Mohammed VI (Morocco)

9. Prince Albert II (Monaco)

10. Sultan Qaboos bin Said (Oman)

11. Prince Karim Al Husseini (Agha Khan)

12. Queen Elizabeth (Britain)

13. Sheikh Sabah al-Ahmad al-Sabah (Kuwait)

14. Queen Beatrix (Netherlands)

15. King Mswati III (Swaziland)

Click here to read more on this story from the Times of London.

Click here to read more on this story from Reuters.