Deutsche Bank, Germany’s embattled largest lender, faces yet another billion-dollar lawsuit. This time it's from one of its biggest shareholders, the fund giant BlackRock.

Several investors claim that Deutsche Bank made led them lose more than $75 billion.

For Deutsche Bank, Europe's largest investment bank that is already dealing with some 7,800 legal cases, another lawsuit might sound rather inconsequential.

This time, however, the plaintiff is none other than one of the lender’s main shareholders.

The U.S. fund giant BlackRock, Deutsche Bank’s second-biggest investor with a shareholding of just over 5 percent, is leading a new multi-billion dollar lawsuit brought by institutional investors. The group claims Deutsche Bank neglected its duties as the administrator of trusts that held residential mortgage-backed securities in the wake of the 2008-2009 financial crisis.

The lawyers for the investors, which also include Allianz subsidiary PIMCO and Prudential, claim that Deutsche Bank’s actions led them to lose collateral worth more than $75 billion. The trusts managed assets totaling $433 billion.

In its role as administrator of trusts, Deutsche Bank had a duty to check the quality of the paper. The investors allege that the German lender knew that the issuers of the derivatives had broken the rules but failed to intervene because it feared other trust administrators might take similar action against derivatives that Deutsche Bank had itself brought to market.

BlackRock and the other banks had no option but to file a suit because if they hadn’t, they would have faced legal action from their own investors.

The Financial Times, which broke the news of this new legal risk for Germany’s crisis-hit flagship bank, cited an unnamed person familiar with the investors’ strategy as saying the compensation claim could amount to several billion dollars.

Both Deutsche Bank and BlackRock declined to comment. Financial sources told Handelsblatt that BlackRock and the other banks had no option but to file a suit because if they hadn’t, they would have faced legal action from their own investors.

Deutsche served as trustee for more than 20 percent of the privately-placed residential mortgage backed securities deals sold between 2003 and 2009, the investors’ complaint said. The bank tried to get the lawsuit dismissed by the Orange County Superior Court last week but judge Gail Andler ruled that the case could proceed.

Despite the fresh bad news, Deutsche Bank’s share price was among the biggest gainers in Germany's DAX index on Tuesday, rising 1.6 percent in morning trading to €13.40. It helped that European banking stocks rose across the board on the day.

That put Deutsche's shares back above the mid-September level when news emerged that the U.S. Department of Justice was demanding $14 billion from the bank to settle claims it sold toxic mortgage-backed securities.

Chief Executive John Cryan is negotiating to get the settlement reduced as much as possible. Fears that the bank may not to be able to afford the payment sent its shares tumbling to a new record low of €9.9 at the start of October.

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Uncertainty over the legal risks facing Deutsche Bank is the main cause of its crisis of confidence this year. The bank has so far set aside €5.5 billion, or $5.98 billion, for litigation costs, but most analysts expect it will have to set aside more in the coming months and years.

Other cases include a potentially expensive money-laundering scandal in Russia, where the bank's staff are accused of helping customers launder some $10 billion.

Germany’s financial regulatory authorities have signaled that in the Russian case, Deutsche Bank may get away with an order to improve its risk management system, but a hefty penalty could still come from the United States. The U.S. Department of Justice and the New York Department of Financial Services have gotten involved to investigate whether the deals in question breached U.S. sanctions against Russia. If they did, the potential fine could soar.

Michael Maisch is currently the deputy editor of Handelsblatt's finance section in Frankfurt. To contact the author: [email protected].