The tennis star first met Meghan in 2010 at the Super Bowl in Miami but the two reunited and befriended each other at the 2014 DirectTV Celebrity Beach Bowl. Williams and her husband Alexis Ohanian attended the royal wedding last year, and the star athlete has publicly voiced her support for Meghan throughout her new life as a royal, from praising her charity cookbook to applauding her for wearing her clothing line.
Serena took a selfie in The Mark's hotel.
Markus Anderson and Misha Nonoo
Markus is one of the former actresses closest friends and was one of the first to meet Harry when the couple first began dating. Anderson is known for his work with SoHo House, an elite, members-only club with luxe locations around the world. Designer Misha Nonoo, another one of Meghan's good friends, was seen arriving.
News anchor, presenter, and author Gayle King was spotted arriving at The Mark Hotel on Wednesday. She wore bright baby pink pumps with a purple coat, and carried gifts for Meghan:
The human rights lawyer arrived at Meghan's party in a red jumpsuit and gold pumps. Reports have said that Meghan and Harry have spent time with the Clooney's at their home in Italy over the summer.
Also in attendance:
Meghan's college friend from Northwestern, Lindsay Roth, arrived at The Mark Hotel in New York for the festivities:
Health and wellness guru, Taryn Toomey, also arrived at The Mark on Wednesday for Meghan's main baby shower.
Meghan's longtime friend and makeup artist, Daniel Martin, arrived at The Mark for the second day of the Duchess of Sussex's baby shower.
WATCH: Meghan Markle Spotted Outside New York City Hotel For Baby Shower.