The executive board of the Port Authority was briefed Thursday on a $1.225 billion joint venture with Westfield Properties for the long awaited retail space at the World Trade Center site.

The Post has learned the 50/50 agreement covers 365,000 square feet of retail space with an additional 90,000 square feet to be added as 2 World Trade Center comes on line.

A written agreement still needs to be hashed out that both boards are expected to approve within the next 90-days. The retail space is expected to open in early 2015.

The deal works out to $3,356 a foot for the first 365,000 square feet and additional monies will be paid for the next 90,000 square feet.

“After being initially involved with the World Trade Center prior to Sept. 11, 2001 and working with Port over the last 10 years we are excited about our partnership with them to rebuild the World Trade Center,” said Peter Lowy, CEO of Westfield America who declined to discuss the financial terms of the deal.

“We will be creating a world class iconic shopping experience for Lower Manhattan and the City of New York in keeping with the other projects we have done in Sydney, London, San Francisco and Los Angeles.”

Westfield had been working with Silverstein Properties and the Port Authority on plans to update the retail mall when the towers were attacked.

It later backed away from the rebuilding when it became mired in politics but reserved the right to jump back in. As the Post has been reporting, those discussions have been ongoing over the last year.

“It’s no surprise but a relief that this is finally done because then they will be able to release information,” said Robin Abrams of The Lansco Corp. “Before it was impossible to get specific information and now everybody will be focused and Westfield will be able to go forward with the brokerage community and specific tenants that have been waiting on the sidelines.”

Abrams called the pricing “hefty,” but in line with what has been going on in the city, and therefore expects the retail space will be priced in the “hundreds of dollars” a square foot. “But it will be the center of the universe down there,” she added.

“The retailers were all waiting to see what would happen at the Trade Center.”