The tennis legend first met Markle met at a charity football game in 2014, and the duo have remained in touch ever since.

Indeed, in a Q&A with William posted to Markle’s lifestyle website The Tig, the soon-to-be royal dished on their friendship, saying: “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 […] and she quickly became a confidante I would text when I was travelling, the friend I would rally around for her tennis matches, and the down-to-earth chick I was able to grab lunch with just a couple weeks ago in Toronto.

Markle added: “We are both the same age, have a penchant for hot sauces, and adore fashion, but what connects us more than those things is perhaps our belief in exceeding expectations – our endless ambition.”

It sounds like the #girlpower friendship to end all others – so why isn’t Williams attending the service?

“I don’t know [if I can go],” the tennis legend said, during a recent appearance on Good Morning America. “I think it’s during one of the tournaments, so I’ll see if I can make it.”

We doubt anyone has ever pulled off the, “I’m not sure, I might be working” card with such blasé charm (although we have a feeling Williams is attending, and has simply been sworn to secrecy)

Whether Williams is there in person or not, though, she fully intends to be at her best friend’s wedding in spirit – and made a point of dishing some key tried-and-tested advice to Markle.

Serena Williams has some ace wedding advice for BFF Meghan Markle