Kammala jumla mai zuwa: Grundström ya koma Marlies don kakar 2018/19. Ya rubuta maki 29 a wasanni 42 don kulob din. A ranar 28 ga Janairu 2019, Grundström (tare da Sean Durzi da wani
2019 zagaye na farko) an yi musayar shi zuwa Los Angeles Kings a musayar Jake Muzzin. Da farko an sanya shi ga ƙungiyarsu ta League ta Amurka, Ontario Reign, amma Sarakuna sun sake kiransa a ranar 9 ga Maris. Ya fara bugawa a wannan daren, kuma ya zira kwallaye na farko na NHL a cikin rashin nasara 4 zuwa 2 ga Arizona Coyotes.