It was their first engagement together without Princes Harry and William and the duo were clearly having a lot of fun.
Kerber, who also won a silver medal at the 2016 Summer Olympics, pulled off the shocking upset to deny Williams her seventh Wimbledon championship.
The sisters-in-law greeted a group of thrilled-looking ball boys and girls, before meeting some junior tennis players.
Immediately following her defeat against Angelique Kerber during the Ladies' Single Final on Saturday, the tennis star gave an emotional interview that expressed her feelings about the heartbreaking loss.
Meanwhile, Williams makes a triumphant comeback to the London tournament, giving birth and battling subsequent health complications just ten months ago, Fox Sports reports.
Nadal-Djokovic: Day 2 beckons
Then came the full trailer in the third set, when Isner's serve was finally broken this Wimbledon after a whopping 110 games. That semi-final only finished just before 8pm making it impossible for Nadal and Djokovic to finish before the 11pm curfew.
They even co-ordinated their outfits, with Meghan opting for Ralph Lauren, in a striped blue and white top, and wide legged silk cream pants. The Duchess of Sussex displaying effortless Hollywood chic in her eye-catching flares.
Kate was wearing a Jenny Packham dress with nude suede heels, and matching handbag.
Photographed entering the stadium, the two ladies appeared to be chatting away happily and giggling with one another.
The 23-time Grand Slam champion attended Prince Harry and Meghan's wedding in May with her husband, Reddit founder Alexis Ohanian. "We've always had a wonderful friendship and every year for a couple years she comes out to Wimbledon, has supported me and now she's supporting me in a different role". "She's an incredible person, Angelique is, and she's a really good friend, so I'm really happy for her", she said.
Williams spoke about her friendship with Markle in a post-match press conference.