In her upcoming memoir, tennis legend Billie Jean King reveals she secretly married her partner Ilana Kloss in 2018.

According to PEOPLE magazine, former New York City Mayor David Dinkins married the couple in his apartment on Manhattan's Upper East Side on October 18, 2018.

King and Kloss, her former doubles partner, have been together 42 years.

In her memoir, titled All In: An Autobiography, King, 77, writes that only a handful of people knew about the marriage, including Dinkins, his wife Joyce, and an aide, who acted as a witness and wedding photographer, plus the City Hall employee who processed their marriage license.

"Nobody threw rice or smashed wedding cake in the other's face," King wrote. "One of the brides wore jeans and a lovely red scarf and the other had on a black shirt, a comfortable warm-up suit, and pearls – ha! – a personal touch of glamour that Ilana still teases me about."

King said that while she felt “very married” to Kloss, she changed her mind about marriage because she wanted to show her trust in her partner.

“But I had a big problem with trusting and it meant a lot to show my trust in Ilana,” King wrote. “Years from now, I never want anyone to question how much I was committed to you.”

Kloss, 65, explained: “So much of our life has been public, keeping this private was something special we could hold on to, just for us.”

All In: An Autobiography arrives Tuesday, August 17.