The feud between the Ambani brothers, two of the world's richest men, has been rekindled by Anil's global ambitions and could become as bitter as the one that split their massive business empire in 2005.
The spark was Anil's bid to merge his Reliance Communications with South Africa's MTN Group to create a global telecoms giant. Older brother Mukesh has objected, saying his permission is required for any sale of the family's shares.
The brothers, Mukesh and the more flamboyant Anil, still live in the same building in an upmarket area of Mumbai and are ranked by Forbes the fifth and sixth richest men in the world respectively, with combined wealth of around $85 billion.
But they had a very public falling out in 2005, three years after the death of their father, legendary magnate Dhirubhai Ambani, which was only resolved when their mother divided the Reliance empire between the two.
Since then, both have grown their businesses significantly, their rivalry simmering but not boiling over until last week.
"I think this time the fight will have more fire," R.K. Gupta, managing director of Taurus Asset Management Co. "Anil has been able to stand on his own legs. I think he was not standing on his own in 2005. It was more of his father's shadow."
Under the deal, sources and media say Anil will swap control of his Reliance Communications for a large stake in the combined unit.
Mukesh's Reliance Industries, India's most valuable company, said it had informed both Anil Ambani's group and MTN "in good faith" that it had first rights over the sale of shares in Reliance Communications.
Reliance Communications has dismissed Mukesh's claim, saying it was based on an agreement signed when the company was under the control of Reliance Industries. Company sources say the firm is prepared for a legal battle.
"Mukesh is using a very sober language and Anil is a bit aggressive, and that aggressiveness shows that he is ready to take on his elder brother," Gupta said.
If they really fancy a battle, analysts say the brothers have much more firepower now than three years ago as their businesses have rocketed in value since the split.
Anil, who runs marathon races, married a film star, mingles with politicians and was the public face of the undivided group, got the newer business.
Since the split, he has overseen spectacular growth in telecoms and mutual funds and expanded into other areas.
His group's Reliance Power raised a record $3 billion in its first offering of shares this year in a frenzied listing that was lapped up by investors in a minute.
Other companies in his group include Reliance Infrastructure, Reliance Natural Resources and Reliance Capital.
Mukesh, who controls the family's flagship firm, Reliance Industries, has a relatively sober image compared to his brother, but stories of his wealth fascinate the media.
He bought a cricket team in a popular domestic league, gave his wife a luxury jet for her birthday, with a bar and fancy showers, and is building a 27-storey home with a helipad for an estimated $1 billion for his family of six, local media say.
But his business success has also made headlines.
Mukesh's group is almost ready with a new refinery which, along with an existing unit, will make its refining complex the biggest in the world. It has also expanded into the retail sector.
This is not the first time since the split that the two have fought. A dispute is still before the courts over the price Anil's group will pay for natural gas from gas fields under Mukesh's control.
"It is not a fight where the brothers are attacking each other directly ... but something like when one tries to do something good the other one is trying to become a hurdle in it," said V.K. Sharma, head of research at Anagram Stock Broking.
The shockwaves of the clash are already being felt in the stock market, where the possibility of a delay in the deal with MTN hit Reliance Communications on Monday.
Its shares ended down 1.5 percent at their lowest close since April 24, having fallen as much as 2.3 per cent during trade.
Reliance Industries ended up 0.7 percent in a Mumbai market that had gained 1.4 per cent.
"More than what impact it can have on the groups' shares, I would say it is bad news for the broader market when there were some signs of a revival after recent falls," said Anagram's Sharma.