Albert von Thurn und Taxis, here with sister Maria, is the youngest billionaire
The world's youngest billionaires have lost nearly a third of their wealth, according to Forbes rich list.
The average net worth of billionaires aged 40 and under is $2.9bn (£2.1bn), down 30% from last year.
The youngest billionaire is Germany's car-racing bachelor Prince Albert von Thurn und Taxis, who is worth about $2.1bn at the age of 25.
His fortune dropped 10% as the financial downturn hit his family's real estate and forestry holdings.
The family's wealth derives from centuries ago when, under the German emperors, they had a monopoly over running the postal system.
According to Forbes, Prince Albert's 30,000 hectares of woodland in Germany is considered one of the largest forest holdings in Europe.
Sergey Brin, 35, Google co-founder, $12bn
Larry Page, 36, Google co-founder, $12bn
Sheikh Mansour Bin Zayed Al Nahayan, 39, Abu Dhabi ruling family, $4.9bn
Daniel Ziff, 37, Ziff Brother Investments, $3.5bn
John Arnold, 35, Centaurus Hedge Fund, $2.7bn
Prince Albert von Thurn und Taxis, 25, $2.1
Kenneth Griffin, 40, Citadel Hedge Fund, $1.5bn
Chu Lam Yiu, 39, Huabao International, $1.5bn
Jerry Yang, 40, Yahoo co-founder, $1.1bn
William Ding, 38, Netease founder, $1.1bn
Andrey Melnichenko, 37, MDM Bank founder, $1bn
His mother, Gloria von Thurn und Taxis, is one of Germany's leading socialites.
The next youngest billionaires are Google founders Sergey Brin, 35, and Larry Page, 36, who have about $12bn each, according to Forbes, which also makes them the richest on the list.
Both have lost just over $6.5bn as shares in Google have dropped 30% in the past 12 months.
The two met at Stanford University before dropping out in 1998 to start Google from a friend's garage.
Jerry Yang, co-founder of Yahoo, scrapes into the list with a personal wealth of $1.1bn. Shares in Yahoo have fallen by 55% since the last list was compiled after the search engine's sale to Microsoft fell through.
Sheikh Mansour Bin Zayed Al Nahayan, the 39-year-old member of Abu Dhabi's ruling family, also appears in the list.
He came to prominence by buying Manchester City football club last year, as well as investing large sums of cash into Barclays bank.
Andrey Melnichenko, the Russian industrialist worth $1bn, just managed to keep his place in the list despite losing 80% of his personal fortune in recent months.
The same cannot be said of Facebook founder Mark Zuckerberg, who drops off the list completely after heading it last year.
Forbes magazine compiles an annual list of the world's billionaires.