“Slumdog Millionaire” director Danny Boyle has hit town with the Oscar-winning film’s writer ­Simon Beaufoy and producer Christian Colson to begin prepping a biopic about Billie Jean King, Page Six has learned.

It will focus on King’s famous “Battle of the Sexes” against Bobby Riggs in 1973.

We previously reported that Boyle turned up at a London premiere of a King documentary right before Wimbledon last year, where most other VIP guests were former female tennis champs.

“No one could figure out why Boyle was there,” cracked a spy.

But, “He and Simon then met with King, and they’re all meeting again in New York to work on the script.” King will then head to the Olympics’ closing ceremonies.