10. Prince Albert II, Monaco

Prince Albert
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Net worth: $1 billion

Prince Albert II of Monaco's net worth reportedly comprises one-fourth of the land he reigns over, as well as an antique car collection, shares in a Monte Carlo resort, a pricey stamp collection, and the Philadelphia-area home of his mother, Grace Kelly, which he purchased in 2016 for an estimated $754,000.

9. Emir Sheikh Tamim bin Hamad Al Thani, Qatar

Emir Sheikh Tamim bin Hamad Al Thani Qatar
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Net worth: $1.2 billion

Emir Sheikh Tamim bin Hamad Al Thani took over the throne of Qatar after his father, former emir Hamad bin Khalifa Al Thani, stepped down in 2013.

The former emir's estimated net worth of $2.4 billion comes from Qatar Investment Authority, which manages the country's oil and gas reserves.

8. King Mohammed VI, Morocco

King Mohammed VI
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Net worth: $2.1 billion

King Mohammed VI's wealth largely comes from his family's ownership of Morocco's National Investment Company, a private holding company that invests in other African countries and operates in banking, telecommunication, and renewable energy.

7. Prince Hans-Adam II, Liechtenstein

Prince Hans Adam II
Eddy Risch/AP Photos

Net worth: $3.5 billion

The Princely House of Liechtenstein's fortune is largely due to its privately owned bank, LGT Group, and investments made through the Prince of Liechtenstein Foundation, which oversees real-estate, forest, and winery assets.

T6. Grand Duke Henri, Luxembourg

grand duke henri
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Net worth: $4 billion

The Grand Ducal Family of Luxembourg doesn't receive a salary but has been granted about $324,851 every year since 1948 to carry out functions — not that they need it, as their net worth is in the billions.

T6. Emir Sheikh Mohammed bin Rashid Al Maktoum, Dubai, United Arab Emirates

Mohammed bin Rashid al Maktoum
Alastair Grant/AP Photos

Net worth: $4 billion

Mohammed bin Rashid Al Maktoum — the vice president and prime minister of the United Arab Emirates and the emir sheikh of Dubai — has spent some of his wealth on charitable donations, such as $10 billion to create the Mohammed bin Rashid Al Maktoum Foundation, which focuses on helping future generations.

4. Emir Khalifa bin Zayed Al Nahyan, Abu Dhabi, UAE

Emir Khalifa bin Zayed Al Nahyan
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Net worth: $15 billion

Khalifa bin Zayed Al Nahyan, the president of the UAE and the emir of Abu Dhabi, has amassed a fortune as chairman of the Abu Dhabi Investment Authority, which manages the UAE's excess oil reserves.

3. King Salman bin Abdulaziz Al Saud, Saudi Arabia

King Salman bin Abdulaziz Al Saud
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Net worth: $18 billion

The source of King Salman bin Abdulaziz Al Saud's wealth comes from his family's ownership of a media group that includes the pan-Arab daily Asharq Al-Awsat and Al Eqtisadiah.

2. Sultan Hassanal Bolkiah, Brunei

Sultan Hassanal Bolkiah
Drew Angerer/Getty Images

Net worth: $20 billion

The sultan of Brunei profits well from the oil and gas industry — he lives in the world's largest palace, which costs more than $350 million, and is said to own more than 600 Rolls-Royces.

1. King Maha Vajiralongkorn, Thailand

King Maha Vajiralongkorn
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Net worth: $30 billion

King Maha Vajiralongkorn and his family made their money from investments derived from the Crown Property Bureau, which manages the property of the crown of the Kingdom of Thailand.

He also owns the 545-carat Golden Jubilee Diamond, the world's largest cut and faceted diamond, according to TIME.