Discharge of functions of President
Section 146(2) · 1999 Constitution (2004 edition)
What Constitution says
(2) Where any vacancy occurs in the circumstances mentioned in subsection (1) of this section during a period when the office of Vice-President is also vacant, the President of the Senate shall hold the office of President for a period of not more than three months, during which there shall be an election of a new President, who shall hold office for the unexpired term of office of the last holder of the office.
This is the 1999 Constitution as published in 2004. Later amendments aren't included yet, so a section may have changed since.
Original source
Official Gazette · CFRN 1999 official PDF · printed page 73–74. Original document
Release: draft-c8d50d87fae9. Source scope, review and corrections