When a reputable Indian news agency declared that Mukesh Ambani had become the world’s richest man on the back of the Bombay stock market’s recent bull run, admirers of the industrialist were quick to celebrate.

A business school in Punjab even rushed to make a cake and distribute sweets to its students to celebrate “the richness” of the 50-year-old man whose personal wealth had apparently overtaken that that of Carlos Slim Helu, the Mexican telecoms tycoon, and Bill Gates, the Microsoft founder. “It is a proud moment for all Indians,” gushed Anshu Kataria, the dean of Aryans Business School.

But the party poppers were hastily put away last night when Reliance Industries, the company chaired by Mr Ambani, was forced to explain that the news agency had got its sums wrong by putting his net worth at $63.2 billion (£31 billion). The correct figure was more like $50 billion, Reliance said, because it had erroneously included the group’s petrol subsidiary in which Mr Ambani does not have a direct holding.

It was embarrassing for all involved, even Mr Ambani, who is used to his every move being chronicled in print. Barely a day passes without reports of his business activities, mainly in petro-chemicals and oil, which run deep in India after he inherited half of the Reliance empire founded by his father. But of late, it is his estranged brother, Anil, who has been stealing the headlines for his audacious launch of India’s biggest initial public offering – a company’s first sale of public shares.

The feud between the Ambani siblings has enthralled Bombay society since their father’s death in 2002 and the division of the family business three years later. Anil’s company, Reliance ADA Group, has the family’s telecoms, finance and energy assets. Hostilities have bubbled to the surface again this week amid claims that Mukesh is trying to undermine his little brother’s big moment. By Forbes magazine’s assessment in February, Anil, 48, was worth $18.2 billion, and Mukesh $20.1 billion, making them the world’s 14th and 18th richest men. Since then, their fortunes have risen to about $38 billion and $50 billion. If they could stand to be in the same room as each other, their combined wealth would put Mr Gates’s $62 billion in the shade.

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