Sita was a Daughter of Ravana according to some versions of Ramayana

In South Indian Ramayan there is mention of Ravan daughter named Swaranmatsya

She was extremely beautiful and charming , golden fish form and used to stay in deep ocean waters
In Thailand and Vietnam golden fish is worshiped
When Hanuman ji and other wanar sena were making bridge to cross ocean
Stone’s were vanishing gradually
Then Hanuman ji went deep into ocean and found that some water amphibians are taking the stones away
There leader was this golden fish
When Hanuman ji tries to take those stone’s , she falls for him
Hanuman ji understands and brings her up
He asked about her family etc , she revealed that she is daughter of Rawan

Hanuman ji tells her father Rawan deeds
Swaranmatsya realises and feeling bad returns all stones ,
And thus bridge was formed without any other problems
Hari Om Sai Ram