Original: All that is known with certainty is that he spent time as a child at both places, and he stipulated in his will that his body be interred at Jerez de los Caballeros, where other members of his family were also interred.
Simplified: All that is known with certainty is that he spent time as a child at both places. In his will, he wanted to be buried at Jerez de los Caballeros, where other members of his family were also buried.