The event, held at New York City's Mark Hotel in February, was thrown by the duchess' pals, Williams, Genevieve Hillis and Jessica Mulroney, according to guest Gayle King, who shared details of the private affair on "CBS This Morning" the day after.
Williams wanted the shower to be just right, she told The Business of Fashion in an interview that took place days after the shower for a story that published online Tuesday.
“Planning something like that takes a lot of effort. I’m a perfectionist, so I’m like, ‘Let’s make it perfect,' " Williams told BoF. “It’s been a lot the last few days.”
And presumably, Williams was happy to do it for her friend, who has shown support for her clothing line, Serena.
While touring Australia with Prince Harry in October, Meghan wore an oversized, plaid blazer from the line.
“It’s so fun because people are like, ‘Oh my God. Like wow, the quality is crazy,' " Williams said to the outlet. “Listen, if we’re giving our stuff to Meghan, it has to be the highest quality that we can get. So, that’s what I tell our team internally: ‘We have to make sure it’s super high quality that, you know, is fit for a royal princess!' "
According to King, Meghan's shower was also perfectly suited for Meghan.
On the morning show, King marveled over the unique shower, where instead of playing the usual games, guests got a lesson on arranging flowers and then created their own arrangements that were donated to different charities through an organization called Repeat Roses.
"I hope she won't mind me sharing this because I've never seen anything like it at a baby shower," King said, adding that the gesture "just speaks to who (Meghan) is. She's kind. She's very generous and a really, really sweet person. I think her friends just wanted to celebrate her."
King also shared that Meghan "didn't open any of the gifts because she wants to do that when she and Harry are back together."
Contributing: Jayme Deerwester
This article originally appeared on USA TODAY: Serena Williams put in 'a lot of effort' to make Duchess Meghan's baby shower 'perfect'