This quintessentially French quarrel was prompted by the announcement last month that the chateau and its vineyards were to be sold to the international luxury goods concern, Louis Vuitton Moet Hennessy (LVMH). When the first writ was issued on Christmas Eve - from one brother to another - the affair started to assume the dimensions of a family feud that could last for generations.
The two sides then started to air their passionate arguments for public delectation, and it became clear that the new year could offer a graphic case study in what happens when exclusive and traditional French companies meet modern international commerce. Despite stiff rearguard resistance from many of the French families concerned, this is a clash that will only become more frequent.
It was on 28 November that the public first heard the news: Chateau d'Yquem, owned by the aristocratic Lur-Saluces family since 1785 and part- owned by them for the previous 200 years, had been sold to the giant LVMH group. The reputed price paid by LVMH for the controlling stake was 500m French francs (pounds 59m).
Reaction to the sale was mixed: from a resigned "that's the only way to survive in this day and age" to profound regret and even anger that so vital a part of France had been betrayed to foreigners.
Almost immediately, however, the sale was contested from inside the family. The older brother, Marquis Eugene de Lur-Saluces, who as well as heading the company is said to have masterminded the sale, was challenged by his younger brother, the Count Alexandre de Lur-Saluces, who has managed the chateau for 28 years.
While acknowledging that he was a minority shareholder, Count Alexandre said that a clause written into the company's statute when he became manager prohibited any change of ownership without his approval - and he did not approve. This is the sense of the writ he issued last week.
The marquis insisted that the family had no choice but sell if Chateau d'Yquem was to survive. He claimed that a majority of the family, accounting for 90 per cent of its shares, were on his side.
The count argued that for the chateau to be controlled by an outside, international interest, was tantamount to betraying the family spirit and would jeopardise standards. For good measure, he accused his brother of being "easily led".
Neither the traditional character nor the standards of Chateau d'Yquem are in doubt. The chateau is a classic fortified farm in the regional style, surrounded by 103 hectares of vineyards in the heart of the Sauternes, south of Bordeaux.
All the grapes are selected and hand-picked only by the most experienced and specialised. It is said that one vine produces only one glass of Chateau d'Yquem. In some years, no vintage is produced because quality is judged too low. The latest vintage, the 1990, is more than F800 a bottle.