In the letter, which starts "Dear Daddy", socialite Gigi Chao asked her father Cecil Chao to treat her gay partner Sean Eav as "a normal, dignified human being" . The pair have been together for nine years and are reported to have married in 2012 in France.
I know it's difficult for you to understand how I could feel romantically attracted to a woman, I suppose I can't really explain it either. It just happens, peacefully and gently," she wrote in the letter, which was published in the South China Morning Post today and was circulated to other Hong Kong media.
Her plea came after property developer Cecil Chao, 77, who refuses to recognise that she is a lesbian, was reported last week to have doubled the "marriage bounty" on his daughter to HKD1 billion (USD 130 million), after an initial offer of HKD 500 million two years ago.
The first sum attracted 20,000 candidates, with the bizarre dowry attempt making international headlines.
In her letter, 33-year-old Gigi said that she forgave her father because he was acting in her best interests.
And she took responsibility for "misleading" him into thinking there might be other options for her.
"I'm sorry to mislead you to think I was only in a gay relationship because there was a shortage of good, suitable men in Hong Kong. There are plenty of good men. They are just not for me."
In a plaintive message to her dad she told him of her sadness that he was unable to share in the life she had made for herself.
"My regret is that you have no idea how happy I am with my life, and there are aspects of my life that you don't share," she said.
Chao, who owns publicly listed property developer Cheuk Nang, is a fixture of Hong Kong high society and regularly appears at public events with his latest young girlfriend. He reportedly once claimed to have slept with 10,000 women.
British movie maker Sacha Baron Cohen is reportedly working on a film based on the story.