user: Question: What is the Birth of the lady that has a Became Duchess on 18 August 1593 husband's accession?
Columns: ['Birth', 'Marriage', 'Became Duchess', 'Ceased to be Duchess', 'Death', 'Spouse']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['11 December 1455', '4 June 1474', '21 July 1495 Created Duchess', "24 February 1496 husband's death", '30 May 1503', 'Eberhard I']
SQL:

assistant: SELECT "Birth" FROM "Table" WHERE "Became Duchess" = '18 August 1593 husband''s accession';