Mexican telecommunications mega-mogul, Carlos Slim, who was named the world's richest man last year, just purchased Duke-Semans Mansion for $44 million.  The Duke-Semans Mansion in New York is a palatial private townhouse on famed Fifth Avenue. The seven story Beaux Arts Mansion is located across from the Met Musuem, boasting 20,000 square feet, 12 bedrooms, 14 bathrooms, and even a doctor's office in the basement.