Mitsui Fudosan is acquiring a 90% stake in 50 Hudson Yards, the 2.9M SF office tower being developed by The Related Cos. and Oxford Properties Group, Reuters reports.

BlackRock, the world's largest asset manager, has agreed to move its headquarters to the building, occupying 847K SF. Construction is expected to cost $3.6B, among the most expensive price tags in New York City history for an office building.

Mitsui and Related secured $1.5B in loans to fund the construction of the tower, but it is unclear how much in equity it will provide. In May, the joint venture behind Hudson Yards, the country's largest private mixed-use development, was seeking $1.8B in construction debt from a partnership between Bank of China, Deutsche Bank and Wells Fargo, The Real Deal reported at the time.

Mitsui Fudosan already owns 92.7% of 55 Hudson Yards, the 780-foot office tower currently under construction. Tenants include law firm Cooley, which just signed a 130K SF lease last month, Silver Lake, Point72 Asset Management, law firm Boies, Schiller & Flexner, MarketAxess and Intercept Pharmaceuticals.

The monolithic 50 Hudson Yards will be one of the biggest office buildings in New York City by square footage, and the densest at Hudson Yards. There is still close to 2M SF of offices available, but Morgan Stanley is reportedly looking for just that much space and has 50 Hudson Yards on its short list.

The tower will start construction immediately, thanks to Mitsui. It was designed by Foster + Partners and will rise to be 985 feet tall, just a foot over the threshold to be designated a supertall.

CORRECTION, SEPT. 11, 10:45 A.M.: Mitsui Fudosan acquired a 90% equity stake in 50 Hudson Yards, but it is not valued at $3.6B, as a previous version of this story incorrectly stated. This story has been updated.