Global miner Anglo American agreed on Friday to buy 40 percent of De Beers from South Africa\'s Oppenheimer family for $5.1 billion (3.7 billion euros), tightening its grip on the world\'s biggest diamond firm. The historic deal will end the involvement of the Oppenheimer family in De Beers, and will take Anglo American\'s stake to up to 85 percent, compared with the current level of 45 percent. \"Anglo American has entered into an agreement with CHL and Centhold International Limited, together representing the Oppenheimer family interests, to acquire their 40-percent interest in De Beers for a total cash consideration of US$5.1 billion,\" the group said in a statement. However, the government of Botswana owns the remaining 15 percent of De Beers and has an option to lift this to 25 percent. \"This transaction is a unique opportunity for Anglo American to consolidate control of the world\'s leading diamond company -- De Beers,\" chief executive Cynthia Carroll added in the statement. \"Today\'s announcement marks our commitment to an industry with highly attractive long term supply and demand fundamentals. \"Underpinned by the security of supply offered by a new 10-year sales agreement with our partner, the government of the Republic of Botswana, this forms a compelling proposition.\" Nicky Oppenheimer, representing the Oppenheimer interests, added that the agreement had been \"difficult\" for the family to reach. \"This has been a momentous and difficult decision as my family has been in the diamond industry for more than 100 years and part of De Beers for over 80 years,\" Nicky Oppenheimer said in the statement. \"After careful and deliberate consideration of the offer, and what is in the best interests of the family, we unanimously agreed to accept Anglo American\'s offer. De Beers, which was established in 1888, is a global leader in the exploration, mining and marketing of diamonds. Carroll said: \"Anglo American is the natural home for our stake as they have been major shareholders in De Beers since 1926 and have a deep knowledge of the diamond business. She noted that De Beers\' management had steered the group through the global financial crisis, adding it was in a \"stable position\" and was \"well placed\" for future growth. Friday\'s deal followed various media reports last year that the Oppenheimer family were close to selling their stake to Anglo.