Kate's hat was designed by Philip Treacy and her shoes by Jimmy Choo.
Kate, 36, gave birth to her third child, Prince Louis, on April 23. Her husband Prince William, 35, served as his brother's best man at the wedding Saturday. The weeks-old little prince was not present at the wedding festivities today.
Kate and Markle have reportedly had a blossoming friendship, with Kate guiding Markle as she transitions into royal life.
In their first interview after announcing their engagement, Harry and Markle addressed the friendship between the former actress and Kate.
“William was longing to meet her and so was Catherine, so you know being our neighbors, we managed to get that in a couple of, well quite a few times now and Catherine has been absolutely," Harry said, with Meghan chiming in to say, "She’s been wonderful.”
Harry added he is grateful for the "fantastic support" of his brother and sister-in-law, describing it as "amazing."
Markle, who was known for her humanitarian work prior to meeting Harry, will join him, Prince William and Princess Kate as a patron of The Royal Foundation.