Following months of industry rumors and speculation, the owners of Calistoga’s Chateau Montelena Winery have sold their respected 40,000-case operation to a revered second-growth Bordeaux wine estate, Chateau Cos d’Estournel.

Spokesmen for Michel Reybier, owner of the Saint-Estèphe winemaking operation, and Chateau Montelena owners Jim and Bo Barrett, said a “firm” deal was reached Tuesday, with regulatory approval of the change of ownership of the medieval-styled stone facility expected by fall.

Jean-Guillaume Prats, general manager of Cos d’Estournel, would neither confirm nor deny a rumored $110 million had been paid for the Napa Valley winery and its vineyards. A spokesman with the Calistoga winery indicated sales figures being bandied about were inaccurate.

“It’s the kind of investment that would be similar to buying a top Bordeaux estate,” Prats told European news organizations.

According to Vic Motto, Global Wine Partners CEO who helped broker the deal, Reybier puts his new wine holding on a par with the best of Bordeaux.

The sale of Chateau Montelena comes about a year after another pair of celebrated Napa Valley wine operations were sold to European wine houses. Stags Leap Wine Cellars and Duckhorn Wine Company were sold in 2007 for $185 million and a reported $250 million or more, respectively.

Ste. Michelle Wine Estates in Washington state and Marchese Piero Antinori of Italy bought Stags Leap. Private equity firm GI Partners, with offices in Menlo Park and London, bought a controlling interest in Duckhorn.

Chateau Montelena and Stags Leap Wine Cellars popped up on the world’s wine radar when a Montelena chardonnay and a Stags Leap cabernet sauvignon beat out their French counterparts in a celebrated comparative tasting in Paris in 1976.

News of the sale comes just days before the Napa Valley premiere of the movie “Bottle Shock,” which reportedly recounts events leading up to and during the so-called 1976 Judgment of Paris tasting. The Barretts, their winemaker at the time, Mike Grgich, and Stags Leap Wine Cellars owner and winemaker Warren Winiarski would become well known throughout the industry and by consumers following the legendary wine competition.

A rich history

Chateau Montelena’s history of winemaking dates back to 1881 when Alfred L. Tubbs planted vines and built a chateau north of Calistoga. In 1886, Tubbs brought a French winemaker on board to make the wine. Within a decade, Chateau Montelena had grown to become the seventh-largest cellar in the valley’s 19th-century winemaking era.

Prohibition effectively ended wine production at Chateau Montelena, although a small amount was produced between repeal and 1969, when attorney Jim Barrett put together a bunch of investors to purchase the property. Barrett restored the chateau, replanted the vineyards, installed new winemaking equipment and brought in a cellar crew to make the first wines in 1972.

Prats said Tuesday that the winemaking teams from Chateau Montelena and Cos d’Estournel will “work alongside” each other for the foreseeable future.

An executive committee — Chateau Montelena winemaker Bo Barrett, Montelena executive director Greg Ralston and Cos d’Estournel winemaker Dominque Arangoits — with Prats serving as president, will oversee the next vintage.

Prats told European news sources that his Bordeaux team would concentrate on existing blends and that he did not have any firm future projects to discuss.

Bo Barrett, who’s spent more than three decades making wines from estate grapes, said Tuesday afternoon that “Michel Reybier understands that it takes time and continuity to learn the true qualities of each place. He understands the importance of continuity, commitment and experience in making world-class wine.”

“This is a perfect fit — a dream marriage,” added winery founder Jim Barrett. “We could not have asked for a finer team to carry on this legacy.”

“The Reybier and Barrett families share a relentless pursuit of quality,” new owner Michel Reybier noted in a prepared press release. “More than anything else, great wine is about place. These two estates are 7,000 miles apart, but share many common qualities and experiences. This is a merging of that experience and both estates will continue to improve over time.”

The achievements of Cos d’Estournel are credited to the man who managed the operation for years, Bruno Prats. In 1998, Prats was forced by French tax laws to sell out to Groupe Taillan, which in 2001 sold it to Michel Reybier, a Geneva-based food manufacturer and proprietor of the La Reserve group of hotels in France and Switzerland.

According to decanter.com, Reybier is chairman of the petroleum company, Pebercan, and St. Tropez Airport Services. His current wealth is estimated at $650 million to $800 million.

Located in the northerly Haut-Medoc commune of St. Estèphe, Cos d’Estournel has no chateau as such, merely a bizarre facade to the winery with huge, elaborately carved oak doors that once adorned the palace of the Sultan of Zanzibar.

Bruno Prats’ son, Jean-Guillaume, manages the estate for Reybier, and the wine is made in the same careful way that his father introduced. The estate is renowned for complex blends of cabernet sauvignon and merlot with silky fruit and marked finesse.

The name “Cos” — with the “s” pronounced — refers to a hill of stones in the Gascon dialect.