This includes following style rules such as not wearing outfits that are too revealing or heels that are excessively high.
When Kate and Meghan have appeared to perform royal duties, all eyes are often on the pair to see what they are wearing, stylist Melita Latham explained.
She told Express.co.uk: “With Kate and Meghan, every inch of their ensemble is examined under the microscope that is the national press.
“Every fold, every button, considered and analysed.”
Both Duchesses have mixed designer pieces with high street outfits and are not afraid to rewear outfits.
No matter what they wear, the royals are sure to bring a lot of publicity to the brands and it has been speculated that they may have received items for free.
However, doing so is reportedly banned by the Royal Family which means Meghan and Kate have probably not worked with any brands.
Although they were not allowed to receive free items or benefit from brand collaborations, Melita explained this is something Zara Tindall has done.
“Whilst not a serving royal, at events she attends Zara gathers all the attention of a royal with very few of the drawbacks,” the expert commented.
“Her dress sense is – of all the royals – quite perfect.
“She can wear rather more daring, sometimes higher hemmed dresses, while also enjoying the casual slinky top and jeans. Her formal wear is exquisite yet relaxed.”
Although Zara is the granddaughter of the Queen, she may not need to follow rules as strictly as she is not a working royal.
Who is Meghan Markle? Quick profile
Meghan Markle was born Rachel Meghan Markle, on August 4, 1981 to parents Doria Ragland and father Thomas Markle.
Her father was previously married to Roslyn Loveless and Meghan has two elder half sibling – sister Samantha Markle and brother Thomas Markle Junior.
Meghan’s first television appearance in the USA was in an episode of the medical drama General Hospital in 2002.
She later moved on to roles in CSI, Without a Trace and Castle along with bit parts in Hollywood films including Get Him to the Greek, Remember Me and Horrible Bosses.
Meghan was also a “briefcase girl” on Deal or No Deal – but her most famous role was as Rachel Zane in legal drama Suits, which launched in 2011.
She was written out in the finale of the seventh series when her character got married, which aired in April 2018 – just before she got married herself.
Charity and humanitarian work
Meghan Markle’s career in television has gone hand-in-hand with her support for causes close to her heart.
She wrote about the stigma around menstrual health in an article for Time magazine and was a Global Ambassador for World Vision Canada – with whom she travelled to Rwanda for the charity’s Clean Water Campaign.
And her commitment to gender equality has seen her work with the United Nations – receiving a standing ovation in 2015 for her speech to mark International Women’s Day.
In September 2011, she wed film producer Trevor Engelson, who she began dating in 2004.
But the pair divorced two years later in August 2013, citing irreconcilable difference.
She was in a relationship with celebrity chef Cory Vitiello for almost two years, before they broke it off in 2016 but the two remain good friends.
And in June 2016, she met Prince Harry on a blind date set up by a mutual friend.
Their relationship began in October that year and just over one year later, on November 27, 2017, the pair announced their engagement.
They married on May 19, 2018 at St George’s Chapel in Windsor Castle.
Some have claimed Meghan Markle is the first mixed-race member of the Royal Family.
Historians are still arguing about Queen Charlotte, the wife of King George III.
But Meghan will be the first royal to openly embrace a mixed-race heritage.
She has written about the difficulties of being a biracial actress in Hollywood as she claims she is not black enough for some roles and not white enough for others.