Marriage settlement and American wealth
The marriage of the Duke and Consuelo resulted in a significant transfer of wealth from the Vanderbilt family to the couple and their descendants throughout the 20th century.
In 1895 the final outcome of the negotiations over the marriage settlement was that the Duke would receive a Trust fund containing 50,000 shares of capital stock of the Beech Creek Railway Company, then worth approximately $2,500,000 ($77,000,000 in 2017) with a minimum 4% dividend guaranteed by the New York Central Railroad Company. After the Duke's death the income would be paid to Consuelo for her lifetime, and thereafter to the holder of the Dukedom (provided that they were also a descendant of Consuelo and the Ninth Duke).
In addition to the Duke's trust fund, William K. Vanderbilt also signed a covenant committing him to providing his Consuelo with an annual income of $100,000 for the remainder of his lifetime; after his death the covenant provided that his Executors would settle a further $2,500,000 trust fund on Consuelo which would be treated as a debt against William K. Vanderbilt's estate.
During the period of 1895 to 1902 the Duke's father-in-law provided approximately $2,500,000 spent to acquire land on Curzon Street and construct and furnish Sunderland House as a London residence for the Duke and Duchess.
Although the couple separated in 1906, further transfers of wealth to the Duke's descendants from the Vanderbilt family included:
The income from a $5,000,000 trust fund created by William K. Vanderbilt in 1912, which would be payable to Consuelo for life and then to her sons by the Duke;
The income from a further $450,000 trust settled on Consuelo, and then her sons by Vanderbilt in 1919;
A $900,000 joint trust fund and outright bequests of $1,000,000 each specified in the will of Consuelo's father for the benefit of her and the Duke's two sons;
A series of bequests in 1978 specified under the will of Consuelo's aunt, Gertrude Conaway Vanderbilt to Consuelo and the Duke's descendants, including:
$100,000 outright and a $400,000 Trust Fund to John Spencer-Churchill, 11th Duke of Marlborough;
A Trust Fund of $1,000,000 to Lord Charles Spencer-Churchill;
$100,000 to Lady Sarah Roubanis;
$200,000 to Lady Caroline Waterhouse; and,
$200,000 to Lady Rosemary Muir.