The reign of Smilec has been considered the height of Mongol overlordship in Bulgaria. Nevertheless, Mongol raids may have continued, as in 1297 and 1298. Since these raids pillaged parts of Thrace (then entirely in Byzantine hands), perhaps Bulgaria was not one of their objectives. In fact, in spite of the usually pro-Byzantine policy of Nogai, Smilec was quickly involved in an unsuccessful war against the Byzantine Empire at the beginning of his reign.

About 1296/1297 Smilec married his daughter Theodora to the future Serbian King Stefan Uroš III Dečanski, and this union produced the Serbian king and later emperor Stefan Uroš IV Dušan.

In 1298 Smilec disappears from the pages of history, apparently after the beginning of Chaka's invasion. He may have been killed by Chaka or died of natural causes while the enemy advanced against him. Smilec was briefly succeeded by his young son Ivan II.