Meghan Markle and Kate Middleton at Wimbledon

The royal sisters-in-law enjoyed their first official outing together without their husbands.

The Duchess of Cambridge and Duchess of Sussex have enjoyed their first official engagement together without their partners, at Wimbledon.

Meghan Markle and Kate Middleton were greeted by cheers as they arrived at Centre Court on Saturday to watch Meghan's close friend Serena Williams play in the women's singles final.

The royal sisters-in-law giggled and gasped through the match, which Williams lost to in straight sets to Germany's Angelique Kerber, just 10 months after giving birth to daughter Olympia.

It was Kate and Meghan's first official outing without their husbands. Image: Clive Mason/Getty Images

It comes exactly two months after Williams took a front-row seat at Meghan's wedding to Prince Harry in Windsor.

Meghan sported a blue and white-striped Ralph Lauren shirt tucked into with wide-legged, high-waisted white pants and white straw boater, while Kate stepped out in a black-and-white Jenny Packham dress with nude suede heels and matching handbag.

Kate and Meghan stopped and spoke with a number of ball boys and ball girls, as well as junior players before making their way across the walkway for lunch.

Kate and Meghan speaking with ball boys and ball girls, as well as junior players. Image: Getty

Also watching from the royal box on Saturday were actresses Emma Watson and Thandie Newton, and actor Mark Rylance.

Williams was the first mother to reach the final since Australian Evonne Goolagong triumphed 38 years ago.

After her semi-final win on Thursday, Williams hailed her "wonderful" friendship with Meghan and said she was looking forward to her attending.

Looking elegant and stylish at the tennis, Kate and Meghan take their seats. Image: Getty

"We've always had a wonderful friendship," Williams told a post-match press conference.

"Every year, for a couple years, she comes out to Wimbledon, has supported me.

"Now she's supporting me in a different role. But our friendship is still exactly the same.

"We always have supported each other, just been there for each other through a lot. I look forward to it."

Centre Court, Wimbledon. Image: Clive Mason/Getty Images

Meghan, who was sitting between Wimbledon patron the Duchess of Cambridge and Gill Brook, the wife of Wimbledon chairman Philip Brook, turned from time to time to speak to Billie Jean King and her partner Ilana Kloss.

With AAP