Two weeks later , John died , but only after persuading his supporters to pledge that they would secure his infant son 's rule .
However , the childless John married Isabella Jagiellon , who gave birth to a son , John Sigismund , in 1540 .
Two weeks later , John Sigismund died , but only after persuading John 's supporters to pledge that they would secure his infant son 's rule .
However , the childless John married Isabella Jagiellon , who gave birth to a son , John Sigismund , in 1540 .