London's Kensington Palace Gardens also know as 'Billionaires Row' is the site of the most expensive house in the world.Lakshmi N Mittal, one of the richest people in the world bought the mansion from Bernie Ecclestone in 2004 for about $10 million USD per bedroom for a grand total of $128 million USD.Hearst Castle in California was built in the 1920's - 30's for William Randolph Hearst at a cost of about $30 million USD, which would equal just under $280 million USD today.Which is the most expensive house in the world? You decide.