FRANKFURT (Reuters) - Stefan Quandt has become BMW's <BMWG.DE> largest single shareholder, giving him a big enough stake to block any potential takeover of the Bavarian carmaker, a regulatory filing showed on Tuesday.

The 51-year-old German entrepreneur's direct ownership increased with shares inherited from his mother, giving him a so-called "blocking stake" of 25.83 percent, worth 13.4 billion euros ($16.6 billion).

Under German takeover rules buyer acquirer own a voting stake of more than 75 percent to gain full control.

The Quandt family has for decades controlled a stake of a little more than 46 percent of the Munich-based carmaker that owns the Rolls-Royce and Mini brands, but Stefan Quandt's enlarged holding means he can now act single handedly to prevent a full takeover, if necessary.

Although the voting rights have been redistributed, the family's stance about keeping its stake remains unchanged, a Quandt family spokesman said.

"The family has no plans to sell their stake," he said.

(Reporting by Edward Taylor Alexander Huebner and Irene Preisinger; Editing by David Goodman)