  Kepler-1647b is the most recently discovered planet that transits two stars,
i.e., a circumbinary planet (CBP). Due to its large orbital separation,
Kepler-1647b stands out from the rest of the Kepler CBPs, which mostly reside
on much tighter orbits near the stability limit. The large separation of
Kepler-1647b challenges inward disk migration as a dominant formation pathway,
suggested by the other Kepler CBPs. In this paper, we consider the possibility
of an undetected planet near the stability limit by examining observational
consequences of such a planet. We calculate the transit probability of the
putative planet, transit timing variations (TTVs) of the known planet, and
eclipsing timing variations (ETVs) of the host binary caused by the putative
planet. We find the presence of a $\gtrsim$30M$_{\oplus}$ inner planet to be
highly unlikely near the stability limit. In addition, we provide future TTV
observation windows, which will further constrain possible undetected planets
with lower masses.
