If at any time the Mayor shall cease to possess any of the aforesaid qualifications of office, or shall be declared legally incompetent, or to be determined by a majority vote of Council to be guilty of malfeasance, misfeasance or nonfeasance in office, it shall be the duty of Council to declare the office of Mayor vacant, and upon such declaration the office of Mayor shall automatically and immediately become vacant. Such declaration by Council shall be made by a majority vote of Council but shall not be finally and officially made until after a public hearing upon the charge or charges brought, and provided further that the Mayor shall have been notified in writing of the charge or charges against him at least fifteen (15) days in advance of such hearing; provided further, that the Mayor and/or his counsel shall have been given an opportunity to be heard, present evidence and examine under oath, all witnesses appearing in support of such charge or charges. To be effective and final, such declaration of vacancy in the office of Mayor must receive the affirmative vote of two-thirds (2/3) of the membership of the legislative authority at the conclusion of the public hearing.