Vanity Fair's September cover story details Princess Diana's relationship with Pakistani heart surgeon Hasnat Khan.
In the article written by contributing editor Sarah Ellison, Khan's family said Diana was "madly in love" with Khan and wanted to marry him.
Khan's cousin said the two talked about life in Pakistan and asked for advice on Pakistani culture.
Ellison reports that Diana sought the approval of Khan's mother and "made it a point to get to know his family."
The article said Diana ended the relationship after Khan refused to marry her or be seen in public together.
This September, parts of Diana's relationship with Khan will be highlighted in the new film "Diana" starring actress Naomi Watts.