The transaction will raise $2.5bn (£1.7bn) for Bertelsmann, six months before it can exercise the "put" option it holds on its stake in AOL Europe.
An agreement between the two companies means that Bertelsmann can sell the stake to AOL for $6.75bn (£4.7bn) after January 2002. When the put option expires, AOL can buy the stake at a later date.
Analysts believe the deal is equivalent to raising short-term debt -- a surprising move, given that the company is understood to have about DM18bn (£5.6m) in cash reserves.
Bertelsmann said it would use the $2.5bn to reduce its debt. In the past, it has said it would use the proceeds from the sale of its AOL stake to fund investment in online content and e-commerce activities.