HAT-P-13c is a substellar object orbiting the star HAT-P-13 located 698 light years away from Earth in the constellation of Ursa Major. A search for transits was negative, however only 72% of the possible transit configurations could be ruled out. With a mass at least 15.2 times that of Jupiter, it may be a massive planet or a small brown dwarf. The gravitational effect of this object on the inner transiting planet HAT-P-13b may allow a precise determination of the inner planet's internal structure.