In view of the failure of his attempts to make a compromise, Siemowit IV finally sent his troops at the Battle of Grunwald, but his participation was only symbolic; in fact, was his son Siemovit V who fielded two banners of his own troops and fought alongside the 'Royal' Poles and Lithuanian troops.
Mengingat kegagalan upaya untuk berkompromi, Siemowit IV akhirnya mengirim pasukannya ke Pertempuran Grunwald, namun keikutsertaannya hanya berupa simbolik, Kenyataannya, putranya, Siemovit V yang mengibarkan dua spanduk pasukannya sendiri dan berjuang bersama pasukan 'Kerajaan' Polandia dan Lituania.