Conversation so far:
Did Devika Rani elope?
The two co-stars developed a romantic relationship, and during the shooting schedule of Jeevan Naiya, Devika eloped with Hassan.
When did this occur?
CANNOTANSWER.
What movie were they working on together?
Jeevan Naiya.
Why did they have to elope?
In the India of that era, divorce was legally almost impossible and women who eloped were regarded as no better than prostitutes and were shunned by their own families.

Question: So one of them was already married?
Self-contained rewrite: So Devika Rani was already married?