A Delaware judge on Thursday blocked Conrad Black's (search) plan to sell control of his publishing empire, Hollinger International Inc., to the Barclay brothers (search) of Britain, saying Black consistently breached his duties to the company.

In a much-anticipated ruling, judge Leo Strine of Delaware's Chancery Court ruled that Black "breached his fiduciary and contractual duties persistently and seriously," adding that his conduct "threatens grave injury" to Hollinger International and its stockholders.

The judge threw out Black's attempts to change the bylaws of Hollinger International (search) in a way that would have tightened his control of the board of directors. Strine also held up defensive measures the company took to block the deal with the Barclays.

The ruling marks a stunning setback to one of the most flamboyant and controversial figures in the newspaper business. Black, who renounced his Canadian citizenship to accept the title of Lord Black of Crossharbour in England, frequently railed against his critics and defended his claim to run the company he founded the way he saw fit.

Pressure began to mount against him last year after minority shareholders raised questions about millions of dollars in payments that Black and his associates received, which the shareholders say should have gone to the company.

Those accusations led to an internal investigation that found that Black and others received $32 million in payments that hadn't been duly approved by the company's independent directors, contrary to statements in the company's regulatory filings.

In an accelerated three-day trial last week, Black took the stand to defend his actions, saying that he had been forced from the CEO suite by his own directors under false pretenses, and had to sell control of Hollinger International's parent company in order to avoid a financial crisis there.

Strine dismissed Black's arguments, saying that he owed a duty to the company to support a sale process that he had agreed to under a restructuring agreement that he signed in November, which also included his removal as CEO.

At the time, Black acknowledged receiving $7 million in payments that hadn't been authorized and agreed to return the money. He later reneged on that agreement and went behind the company's back to reach a private deal to sell his controlling stake in the company to the Barclay brothers, twins who control hotel, retail and newspaper businesses from a small island in the English Channel.

Strine ruled that Black "immediately violated" his obligations under the restructuring agreement by applying himself "in a cunning and calculated way" to reach a deal with the Barclays.

Strine said Black misrepresented facts to Hollinger International's board, used confidential company information to further his own goals and made a series of threats against the company's independent directors.

The ruling found that the Barclays deal would prevent the company from realizing the benefits of the formal sale process that Black had agreed to support.

The case was being tried in Delaware because Hollinger International, like many U.S. companies, is legally based there.