Millennium Partners has the green light to control 1.2 million more square feet of residential, office and retail space in Boston’s Downtown Crossing.

The firm, developer of the downtown Ritz-Carlton and two other Downtown Crossing projects under construction, has agreed to take the controlling stake as developer of the demolished Filene’s site.

The project, likely to cost $500 million, is expected to reach 500 to 600 feet in the air and include retail, office space and hundreds of residences. It will be at least a year before construction starts, largely because of paperwork the developer will need to file with the city, community meetings and design alterations that will likely ensue.

The firm takes over the project from Vornado Realty Trust, now merely an investor in the project. Vornado got on the bad side of Mayor Thomas Menino and Boston after it failed to build anything following the demolition of the iconic Filene’s building.

"We were actually interested in this site before the current owner bought it," said Philip Aarons, Millennium founding partner. "This is an area we’ve invested in. It’s an area we believe in."

Besides the downtown Ritz and Ritz residences, the firm’s 265-unit Millennium Place III is under construction property across from the Ritz. The developer also recently began construction of Hayward Place, another residential project in Downtown Crossing.

"This is a priority for Millennium because it’s their own money that’s at stake," Mayor Menino told Banker & Tradesman, referencing the fact that Vornado is a publicly traded company. "I have great faith in their priorities for this. It will be a landmark in the city."