Star Wars Adventures #18 showed us how Han Solo lost the Millennium Falcon to Ducain, an event he mentioned in The Force Awakens.

Gannis Ducain^[3] was a Kajain’sa’Nikto^[1]male^[2]gunrunner who stole the Millennium Falcon from Han Solo, only to have it stolen from him later by the Irving Boys.^[4] Ducain added a rotating core to the ship’s gun well.^[3] In 34 ABY, after Solo and his First Mate Chewbacca recovered the Falcon, Chewbacca started to fix the unadvised modifications made by Ducain whilst Rey was trained by Jedi MasterLuke Skywalker on Ahch-To.^[5] During her search for the Falcon, Bazine Netal was told by LadyProxima to travel to Jakku to speak with Ducain about the ship.