ALBANY — State Senate Majority Leader Andrea Stewart-Cousins revealed Thursday she was blindsided by a deal Gov. Kathy Hochul reached to commit a whopping $850 million in public money for a new Buffalo Bills stadium.

Under the agreement — announced Monday following weeks of behind-closed-doors meetings involving Hochul, Erie County officials and the franchise’s owners — New York State will dedicate $600 million in the proposed $216 billion 2023 budget for the venue’s construction, Erie County will cover $250 million and The NFL and the Bills will pay $550 million.

Asked if she knew about the specifics of the $1.4 billion project before they were released, Stewart-Cousins (D-Yonkers) replied, “No.”

“Well, I mean, we were discussing it. I think we’re still trying to figure out what the parameters are,” she told reporters in Albany’s Capitol outside her office when asked for her reaction to being left in the dark. “So we’re discussing it.”

The Post reported earlier this month that state and county officials would spend nearly $1 billion for a new Bills stadium. For the project to break ground, state lawmakers will need to approve the stadium funding when they cast votes on the annual budget.

The new Bills’ home field — set to replace the decades-old Highmark Stadium by 2026 — is one of the main sticking points in the negotiations regarding the soon-to-be late budget, along with New York City casinos and bail reform.

Asked about criticism that the project is a publicly subsidized handout to billionaires — let alone ones who live in Florida — Stewart-Cousins declined to throw a penalty flag, vowing to “take a look at” the particulars, while talking up the significance of the Bills’ significance to Buffalo and Empire State.

“So we actually have the parameters, I’m not in a position to really talk about it, other than the fact that clearly it is now being discussed. We’re going to get the language. We’re going to take a look at it,” the lawmaker said Thursday afternoon. “But I think that we all know that the Buffalo Bills are important, not only to Buffalo, but to the state, so we’re looking at it, but I don’t have the language yet.”

In addition to the opaque process ahead of the deal’s announcement and complaints about corporate welfare, the project has come under fire because the governor’s husband, Bill Hochul, could potentially stand to benefit from it, as The Post reported Tuesday.

Bill Hochul is senior vice president and general counsel for Delaware North, the major food concessionaire at the Buffalo Bills’ current Highmark Stadium. The agreement requires that the team remain in Buffalo for another 30 years.

“One of the biggest winners of this bad stadium deal is Delaware North. Delaware North will make far more money from additional new food service and beverage business in the new stadium,” John Kaehny, executive director of the government watchdog group Reinvent Albany, previously told The Post.

On Wednesday, former state officials who worked for disgraced ex-Gov. Cuomo Andrew Cuomo ripped Hochul for agreeing to give the owners of the Buffalo Bills $600 million in taxpayer funds to build a new stadium that won’t be located in New York’s second largest city. A state official familiar with preliminary discussions for a new Bills’ stadium said Cuomo wanted it built in the City of Buffalo instead of the suburban Orchard Park, where the current stadium is located.

“We would not have done a deal with a stadium in the suburbs. It had to be in downtown Buffalo,” said a former Cuomo official familiar with the discussions. “We would have never given that much. The deal doesn’t make any sense.”

Stewart-Cousins’ Thursday comments come as legislative leaders and Hochul will miss their midnight budget deadline as state lawmakers prepare to leave Albany for a long weekend until they reconvene next week. If they pass a budget by Monday at 4 p.m., New York will “avoid any issues with upcoming payrolls” of state workers for the new fiscal year, according to state Comptroller Tom DiNapoli’s office.