Write SQL query to solve given problem: For all cities where Seine is located at, which city has the greatest population? Calculate the difference from the city with least population.. Keep the solution inside sql tag ```sql [SQL-Query] ```
SELECT MAX(T1.Population) - MIN(T1.population) FROM city AS T1 INNER JOIN located AS T2 ON T1.Name = T2.City INNER JOIN river AS T3 ON T3.Name = T2.River WHERE T3.Name = 'Seine'