Celebrated across the Commonwealth, the day is an opportunity for each of the institution's 53 member states to highlight the positive values of the family of nations.
Town and Country magazine described Markle's appearance at the event as a "striking display of British patriotism", noting that she sang along to the national anthem of the United Kingdom, "God Save the Queen".
"Through exchanging ideas, and seeing life from other perspectives, we grow in understanding and work more collaboratively toward a common future", said the Queen.
Amanda Wakeley's site describes it as "elegant, rich cream outerwear" and a "a chic cover-up as the weather turns warmer".
Known in the local press as the "Fab Four", Markle, Prince Harry, Prince William and Catherine are to meet with schoolchildren after the service.
One teacher told the Daily MailMarkle shared her joy about the couple's upcoming wedding, to be held at Windsor Castle.
Cheryl's partner Liam Payne performed at the service, while Dr Andrew Bastawrous, an eye surgeon who has helped combat blindness in developing counties, gave a reflection.
Queen Elizabeth II joined the ceremony alongside Prince Harry and his fiancee Meghan Markle in London today. While her coat costs $1,199, the dress is being sold a discounted rate of $267 (it usually retails for $680).
Additionally, Harrold says she's learning etiquette and protocol "from within", and the royal family has made it "very easy for her to just ask the question as she goes along".
Reports quickly emerged that Meghan's reclusive dad Thomas Markle wouldn't be escorting her down the aisle as he felt too shy to do the job.
The former Suits star also remarked on the "beautiful" service while speaking to a religious education teacher from Newcastle, adding that she had especially enjoyed the music.
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