user: Question: Name the birth of the person that has a spouse of Frederick IV and became consort of 4 April 1721
Columns: ['Birth', 'Marriage', 'Became Consort', 'Ceased to be Consort', 'Death', 'Spouse']
Types: ['text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['1430/31', '28 October 1449', '28 October 1449', "21 May 1481 husband's death", '10 November 1495', 'Christian I']
SQL:

assistant: SELECT "Birth" FROM "Table" WHERE "Spouse" = 'Frederick IV' AND "Became Consort" = '4 April 1721';