The sale of the stake is part of an agreement the company made with AOL in 2000, which will see the media and internet giant take 30% of AOL Europe now for £3.7bn and the remainder for £1bn in July.
Bertelsmann spokesman Oliver Herrgesell said: "We aim to expand the television business in Europe and our music unit, and are looking for possibilities to boost our US publishing business."
The company agreed last month to buy Pearson's 22% stake in European broadcaster RTL, in which it already has a 67% holding. Yesterday, it revealed it had offered 44 a share for the remainder of RTL it does not already own.
However, a stock market offering of Bertelsmann would break decades of tradition at the company, which was born in the 1970s out of the publishing company founded by Carl Bertelsmann in 1835.
The company's ownership is currently split 17.3% to the Mohn Family, 57.6% to the Bertelsmann Foundation and 25.1% to Group Bruxelles Lambert. Its flotation, which has been mooted for several years, has become a contentious issue because the company would not be able to use shares as currency in acquisitions.
However, chief executive Thomas Middelhoff announced his plans in June to restructure the business with the aim of improving margins and achieving a return of at least 10% on annual sales. The company could sell shares as early as next year.
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