Much has been talked and written about Mukesh Ambani's 27-storey house, Antilia. Now the question is why has the family not moved into the house, even though it looks lived in.
The New York Times reports that the owner, Mukesh Ambani, and his spokesman have declined to discuss the matter, leaving the theorists plenty of room to ruminate.
One popular explanation is that, despite the time and money lavished upon it, the building does not conform to Vastu Shastra.
The NYT report said, at night, the cantilevered tower is lit up bottom to top, inside and out.
Members of the city's moneyed class report attending movie screenings in the theater and eating dinners in the grand ballroom, served by a staff trained by the luxury Oberoi hotel chain.
Yet, friends of the family say that after the last canapés have been served and the guests bidden goodbye, the Ambanis often decamp to Sea Wind.
That is the more modest, 14-story apartment tower at the south end of the city that Ambani, his wife, Nita, and three children, share — on different floors — with his mother and his estranged younger brother, Anil, and his family.
When does Mukesh Ambani plan to actually move into Antilia?
"I have asked him the question twice," a friend who has attended several parties there told NYT.
He asked not to be identified for fear of ruining his relationship with Ambani, whose net worth Forbes has estimated at $27 billion.
"He said, 'Yes, we'll go next month. Let it be done.' They don't talk about it."
Another close family friend confirmed to NYT that the Ambani family did not live at Antilia but said they did sleep there "sometimes." This friend, who also insisted on anonymity to avoid offending Mr Ambani, had no explanation.
Tushar Pania, a spokesman for Mr Ambani's company, Reliance Industries, dismissed questions about whether the family was living at Antilia as idle gossip.
"It's a private home. There is no reason to discuss it in public."
He said the family had moved in, but when asked whether the family still lived at Sea Wind, he revised: "They live in both places."
But why would someone build what is widely considered the world's most expensive private residence and then use it as a pied-à-terre?
Some friends, business associates and Ambani watchers posit the Vastu explanation, which gained wider currency earlier this year when DNA, an English-language newspaper in Mumbai, published an article about it citing "sources in the know", writes NYT.
Antilia, on upmarket Altamount Road in south Mumbai, reportedly has six floors of parking, swimming pools, a ballroom, a cinema and three helipads.