user: Question: Who is the Monarch whose Heir is Robert Curthose when the Reason is that the father became king?
Columns: ['Heir', 'Status', 'Relationship to Monarch', 'Became heir', 'Reason', 'Ceased to be heir', 'Monarch']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['Robert Curthose', 'Heir presumptive', 'Son', '1066', 'father became king', '1077', 'William I']
SQL:

assistant: SELECT "Monarch" FROM "Table" WHERE "Heir" = 'Robert Curthose' AND "Reason" = 'father became king';