Thailand's King Bhumibol lost $5 billion last year.
The 81-year-old monarch - who is currently the richest royal in the world - saw his fortune drop to $30 million as a result of the global financial crisis.
But Bhumibol was not the only wealthy royal to lose money in the credit crunch.
Of the 15 monarchs who made the 2008 Forbes magazine list of the World's Richest Royals, 12 have seen a drop in their net worth.
Combined, they have lost over £22 billion.
One of the worst affected is United Arab Emirates' Sheikh Mohammed bin Rashid Al Maktoum, whose fortune is down by an estimated $6 billion as a result of the declining real estate market.
Dubai's ruler Shiekh Khalifa bin Zayed Al Nahayan didn't fare much better, losing $5 billion after oil prices plummeted.
The loss sees him slip from second to third on the list of the wealthiest monarchs.
Monaco's Prince Albert II lost $400 million as a result of falling real estate and art prices, while The Netherlands' Queen Beatrix and her sons reportedly lost $100 million on the stock market.
Just two monarchs - Brunei's Sultan Haji Hassanal Bolkiah and Qatar's Sheikh Hamad bin Khalifa Al Thani - saw no change in their fortunes.
The only ruler who managed to make money in the past year is Morocco's King Mohammed VI, who made $1 billion in the lucrative phosphate market.
Forbes magazine's World's Richest Royals:
1. Thailand's King Bhumibol, $30 billion (down $5 billion)
2. Brunei's Sultan Haji Hassanal Bolkiah, $20 billion (no change)
3. United Arab Emirates' Sheikh Khalifa Bin Zayed Al Nahayan, $18 billion (down $5 billion)
4. Saudi Arabia's King Abdullah bin Abul Aziz, $17 billion (down $4 billion)
5. Dubai's Sheikh Mohammed Bin Rashid Al Maktoum, $12 billion (down $6 billion)
6. Liechtenstein's Prince Hans-Adam II, $3.5 billion (down $1.5 billion)
7. Morocco's King Mohammed VI, $2.5 billion (up $1 billion)
8. Qatar's Sheikh Hamad bin Khalifa Al Thani, $2 billion (no change)
9. Monaco's Prince Albert II, $1 billion (down $400 million)
10. Aga Khan's Prince Karim Al Husseini, $800 million (down $200 million)
11. Oman's Sultan Qaboos bin Said, $700 million (down $400 million)
12. Britain's Queen Elizabeth II, $450 million (down $200 million)
13. Kuwait's Sheikh Sabah Al-Ahmad Al-Jaber Al Sabah, $400 million (down $100 million)
14. Netherlands' Queen Beatrix, $200 million (down $100 million)
15. Swaziland's King Mswati III, $100 million (down $100 million)
USA
Your Talkback on this Story