Conversation so far:
What is Mughal empress?
Upon his accession to the throne, Shah Jahan designated Mumtaz as his chief empress with the Mughal empress title of Queen of the World and Queen of the Age.
Where was Mumtaz Mahal the empress?
Mumtaz Mahal was the empress of the Mughal Empire
When did Mumtaz Mahal become empress?
Mumtaz Mahal became empress in 1628
How long did Mumtaz Mahal serve as empress?
Mumtaz Mahal's tenure as empress was brief, spanning a period of only three years due to her untimely death.

Question: How did she die?
Self-contained rewrite: How did Mumtaz Mahal die?