There was an issue of a royal charter during July 26, 1324 which was the first document that had a reference of Basarab's existence. The charter accordingly said that Basarab and Wallachia were a subject of Charles I of Hungary as voivode of Wallachia. Basarab was "disloyal to the Holy Crown of Hungary" in 1325 when he seized Banate of Severin and raided the common southern regions of the Kingdom of Hungary where Basarab supported Michael Shishman of Bulgaria's attack on the Kingdom of Serbia, but the armies united together in strength and forced were defeated in the Battle of Velbazhd on July 28, 1330. Soon, Charles I of Hungary then invaded Wallachia where Wallachians ambushed and annihilated most royal troops in the Battle of Posada when it occurred between the 12th and 9th of November,