user: Question: When did the duchess who became duchess on 7/8 April 1766 cease to be duchess?
Columns: ['Name', 'Birth', 'Marriage', 'Became Duchess', 'Ceased to be Duchess', 'Death', 'Spouse']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Maria Josepha of Bavaria', '30 March 1739', '23 January 1765', "18 August 1765 husband's accession", '7/8 April 1766 Title passed to sister-in-law', '28 May 1767', 'Joseph II']
SQL:

assistant: SELECT "Ceased to be Duchess" FROM "Table" WHERE "Became Duchess" = '7/8 April 1766';