King founded the Women’s Tennis Association (WTA) in 1973 but wants it to combine with the men’s Association of Tennis Professionals (ATP) to form a unified world tour.

Twenty-time Grand Slam champion Roger Federer sparked a fresh debate earlier this year when he called for men’s and women’s tennis to be "united", suggesting the time had come to bring the two tours together while the season was suspended due to the COVID-19 pandemic.

King does not believe an ATP-WTA merger will happen in the "near future" but reckons tournaments make "a lot more money" when men and women play at the same event.

"I tried to get us together back in 1968 and 1970 and the men rejected us," King said.

"Roger Federer just brought it up not too long ago, saying that men and women should be together.

"I have always felt that if we were together, we would have one voice and not just what we can do on the court but what we could do for the world off the court as one.

"I don’t think it is going to happen in the near future, but I wish I did."

Aside from the four Grand Slams, the Italian Open - which is currently underway in Rome - is among a handful of tournaments where the ATP and WTA players both feature at the same time.

"Just from a pure business point of view, when you have the men and women together the tournament is worth a lot more money," King added.

"I think we need to discuss that more often.

"The men always say that they are so big about business and yet they are the ones that don’t want us to be together when we should be.

"But it is okay, let’s keep moving.

"At least with the ITF [International Tennis Federation] we have the Davis Cup and Fed Cup and then the Olympic Games at the top."

The Fed Cup has been renamed the Billie Jean King Cup in recognition of the 76-year-old’s contribution to tennis on and off the court.

King won 39 Grand Slam titles including 12 in singles, 16 in women’s doubles and 11 in mixed doubles.

She has also been a campaigner for equal pay in the sport, leading all four majors to offer the same prize money to men and women. 

"No one wants to be discounted by gender, colour or sexual preference," King said.

"When we get less prize money it says we are worth less. Everyone matters.

"When you have equal, the inclusion is beautiful, but when you don’t it is a horrible feeling.

"Women have always been paid less than men in real jobs so that’s why we want more women on boards and more women in the media as we want to reflect what the world looks like.

"It’s very important for everyone to have equality and to be appreciated and included."

King is also a big fan of recently-crowned US Open champion Naomi Osaka’s efforts to raise awareness of the Black Lives Matter movement.

The 22-year-old three-time major winner wore seven masks each bearing the name of a black American who was a victim of police violence or racial injustice before and after every round on the way to winning at Flushing Meadows.

"I love Osaka because when she is interviewed she actually looks at the interviewer, you can tell she is authentic and gives heartfelt answers," King said.

"It is so great when you see the young people out there, pushing.

"Black lives do matter so I think it’s amazing what Naomi is doing and just think she is 22 years old, so she is just getting started.

"The biggest difference from the old days ago to now is technology.

"Technology has changed everything.

"I am so happy she is using all the possibilities that she has."