Chivas Brothers had created what was to become the world's leading premium Scotch Chivas - Chivas Regal.
The first was exported to United States in 1909, and is still at the very forefront of the Chivas Brother's brand portfolio.
In 1949 Chivas Brothers was acquired by Seagram Distillers Plc.
Glen Grant whisky had long been used for blending into Chivas Regal.
To back up Seagram's promotion they have spent hundreds of thousands of pounds turning Strathisla distillery into their flagship visitors' centre for their Chivas Regal blend while essentially retaining the quiet individuality of its elegant bildings.
Another Seagram distillery Allt-a-Bhainne built in 1975 solely to give malt for the company's blends including Chivas Regal.

Chivas Regal contains around 40 percent malt from where it's including 4 percent Strathisla also owned by Chivas.

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Source www.bbr.com :

Chivas Regal

Chivas Regal is a  blended Scotch whisky produced in Strathisla in Speyside. The name "Chivas" comes from Gaelic seamhas, meaning lucky, or blessed with fortune.

The brand was founded by brothers James and John Chivas, owners of a fine products store in Aberdeen , that stocked exotic spices, rum and coffee and rare French brandies.

They started producing a blended whisky that in their words would be “easy-drinking and perfect to enjoy and share amongst friends”. Word of their new whisky soon spread and in 1843 they received a Royal Warrant by Queen Victoria.

One of the most important of these Speyside malts is Strathisla, produced at the oldest distillery in the Highlands of Scotland - Strathisla Distillery. Strathisla imparts the rich and generous taste of honeyed fruit and creaminnes.

All Chivas Regal blended whiskies are aged for at least twelve years. In 1997, Colin Scott, the master blender created a new blend of aged whiskies to produce Chivas Regal 18 Year Old.