Venus Williams has been confirmed for the 2017 ASB Classic, joining her sister Serena at the Auckland event.
The elder Williams has been a regular here for the last three years, winning the event in 2015 after the reaching the final a year earlier.
With reports that the ASB Classic are also close to reaching a deal with Caroline Wozniacki and Ana Ivanovic, it gives next year's event an unprecedented level of star quality.
It's also a bit of a surprise, as the Williams sisters often don't play at the same tournament outside Grand Slams and Premier Mandatory events like Indian Wells and Miami.
"It really is incredible," said tournament director Karl Budge. "I couldn't believe it when we signed Venus four years ago for the first time. To have them both coming is absolutely mind blowing for an event of our size. It really goes to show how respected we are."