Hazel Decided to Talk

When Alex found Hazel again, the girl was alone in the dark. His steps halted as he watched Hazel bent forward with both hands on her knees. Alex blew a breath of relief when he found her safe and sound. He took a step towards her and stopped again, wondering if he should leave her alone. 

He had heard a few words of his classmate's discussion and knew that Hazel was upset.

A few years ago, his mother had once told him about what had happened to Hazel and her family. It was Hazel's parents' death anniversary and he saw how her mood was a little off. Alex was worried about Hazel, and it was at this time that his mother told him that if he really liked Hazel, he has to treat her well and never bully her. Hazel was a pitiful girl and had suffered a lot of grievance from a young age.

When Alex found out how Hazel had lost her parents, he was unable to react.

How old was Hazel when she lost both parents at the same time?