By the second half of the 1340s, little remained of Ivan Alexander's initial successes. John VI Kantakouzenos' Turkish allies pillaged parts of Bulgarian Thrace in 1346, 1347, 1349, 1352 and 1354, to which were added the ravages of the Black Death. The Bulgarians' attempts to repel the invaders met with repeated failure, and Ivan Alexander's third son and co-emperor, Ivan Asen IV, was killed in battle against the Turks in 1349, as was his older brother Michael Asen IV in 1355 or a little earlier.