Fortress has formed a strategic alliance with Mount Kellett to create an investment company with more than $75bn (£49bn) in assets under management.
The deal sees an affiliate of Fortress become co-manager with Mount Kellett of its investment accounts and related accounts.
The move comes as Mount Kellett, which was formed by former Goldman Sachs banker Mark McGoldrick in 2008, struggles to recover from a fall in the value of its investments in the oil industry.
McGoldrick has long had a close relationship with Fortress and is a close friend of its co-chairman, Peter Briger.
According to those familiar with the business, the future of Mount Kellett’s EMEA real estate team is unclear as staff share considerable overlaps with Fortress’s existing expertise.
In addition, Mount Kellett’s EMEA investment activity had been limited in recent months.
Staff are to be updated before the deal closes on 30 June.
