UBS' largest shareholder, Singapore's sovereign wealth fund, said it is trimming its stake in the Swiss bank to less than 3 percent. The secretive state fund was mum on its reasons for the move.

Singapore was one of UBS' staunchest allies during the financial crisis, when the Swiss bank had to tap shareholders repeatedly as $50 billion in losses on illiquid mortgage securities piled up.

Now, the Government of Singapore Investment Corp., or GIC, will sell the bulk of its stake in UBS, into which it had poured 11 billion Swiss francs in 2007. GIC had little joy with the investment, through convertible notes, initially: UBS was forced to accept a government-led rescue package one year later.

From Bad To Worse

The notoriously secretive sovereign wealth fund dug in for the subsequent years, which went from bad to worse. In 2010, the bank began righting itself through several restructuring efforts aimed at limiting its investment banking business and boosting its capital as well as its wealth management activities.

«UBS has been informed by GIC Private Limited that it intends to sell up to 93,000,000 existing shares in UBS, equivalent to 2.4 percent of the outstanding shares and voting rights in UBS Group through an accelerated book-build offering to institutional investors,» UBS' investment bank said in a statement.

The sale takes Singapore's stake in UBS to less than 3 percent, from more than 5 percent. This effectively means that the GIC had already lowered its stake: in 2014, Singapore owned 7.07 percent of the Swiss bank, but a minimal drop in shares would not be required to be publicly disclosed.

Blackrock Biggest Shareholder

The GIC, which has rarely spoken publicly about the investment, gave no reason for the move. Its bosses have quietly made clear their distaste for the various scandals – tax evasion, money-laundering, and rigging of foreign exchange, benchmark interest rates and precious metal prices.

The move leaves Blackrock as the largest shareholder in the Swiss bank, which is now in rude health. The U.S. asset management giant owns 4.89 percent of UBS' shares.