Softbank, a Japanese telecoms and technology group, has finalised its acquisition of New York private equity and credit fund manager Fortress Investment Group to create the centrepiece of a striking move into investment management.

The $3.3bn deal, announced in February, means Fortress, which was founded in 1998 by former BlackRock executives Wesley Edens and Randal Nardone, is now a fully-owned subsidiary of the ambitious and fast-growing Japanese telecoms conglomerate. The group holds stakes in businesses stretching from Chinese internet retailer Alibaba to UK chipmaker ARM.