As RogerWS76 said above, the reigning Queen takes the title of Queen and her husband is known as Prince... or referred to as the Queen's Consort.
Traditionally a reigning King's wife would take the title of Queen. It has been suggested that Camilla, Duchess of Rothesay might not take the title Queen when her husband becomes King because both of them have previously been married and divorced, and that she would be regarded as the King's Consort.
Whether this would set a precedent for the next generation remains to be seen. Personally I would have thought not and that Kate would take the title of Queen.