Olympia's selection of garments include a tracksuit, three dresses, Gucci sneakers, overalls, and a t-shirt featuring her superstar mother in the middle of a tennis match. Picture: Instagram

Serena Williams thinks her friend Duchess Meghan will be "the best mom".

The 37-year-old tennis champion - who has 20-month-old daughter Olympia with husband Alexis Ohanian - has been pals with the former 'Suits' actress since 2014, and she's confident she is going to take to motherhood easily when she welcomes her first child with husband Prince Harry into the world in the coming weeks. 

Asked how she will cope with parenthood, Serena said: "She'll be the best mom, for sure."

The sports superstar - who attended Meghan's New York baby shower in February, along with the likes of Amal Clooney, Gayle King and Jessica Mulroney - also opened up about the challenges of being a first-time mom and how she had to learn to "go with the flow" and adapt to living day-to-day without too much planning to avoid causing unnecessary stress. 

She added to E! News: "Accept mistakes and don't expect to be perfect. We put so much pressure on ourselves.

"I had all those high expectations and what I was going to do and then I had what I was going to do. 

"I was gonna recover and I was gonna be great, and this is a time that everything is not going to go as planned. 

"My whole life is so planned and this is the one time where it wasn't. You just gotta go with the flow."

The 37-year-old royal - who tied the knot with 34-year-old Harry on May 19, 2018, at St George's Chapel at Windsor Castle in front of their famous friends and the royal family - previously gushed about her friendship with Serena and how they met during a charity football game in a post on her old blog The Tig.

She wrote: "We hit it off immediately, taking pictures, laughing through the flag football game we were both playing in, and chatting not about tennis or acting, but about all the good old fashioned girly stuff.

"So began our friendship."