Walmart heiress Alice Walton is rumored to be the mystery buyer of the $70 million “Jewel of Fifth Avenue,” the most expensive co-op in NYC history.

Walton, worth $34.9 billion, is whispered to have purchased the penthouse at 960 Fifth Ave. that belonged to the late Seagram honcho Edgar Bronfman Sr.

The Post reported that the prewar pad hit the market last month, prompting a bidding war between two wealthy clients.

The first hopeful was ready to put down $65 million, the full asking price, when the mystery buyer swooped in with $70 million.

Art collector and horse breeder Walton, who lives on a ranch in Millsap, Texas, was not reachable.

Broker Brown Harris Stevens declined to comment.