This is how Prince Harry and Meghan Markle marked Princess Diana's birthday

The Duke and Duchess of Sussex enjoyed a day out at the Audi Polo Challenge at Coworth Park in Ascot

The Duke and Duchess of Sussex enjoyed spending some quality time together watching the polo on Sunday, on what would have been Princess Diana's 57th birthday. The royal couple were spotted at the Audi Polo Challenge at Coworth Park in Ascot for the second day in a row, with pictures published online showing Meghan looking effortlessly stylish in an oversized white shirt and black skinny jeans, while carrying a white sun hat and a pair of statement shades. Harry, meanwhile, who was watching rather than playing on Sunday, also looked casual in a grey polo shirt and white trousers. Meghan accessorised her look with a bag which she wore cross body, a royal style rule she has previously broken – and nailed – during her very first visit to Scotland in February when she and Harry undertook a royal engagement to Edinburgh.

Meghan Markle and Prince Harry were out in Ascot on Princess Diana's birthday

On Saturday, Meghan and Harry were in Ascot, and Meghan took along her good friend Serena Williams to cheer on Harry and Prince William who were both competing in the event. Also in attendance were some of the world's top polo players and VIPs including Tom Holland, Anna Friel and Dominic Cooper. The high society sporting event supports two charities close to the royals' hearts - Child Bereavement UK and Tusk Trust.

MORE: Meghan Markle takes Serena Williams to watch Prince Harry and Prince William at the polo

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Last year to mark their late mother's birthday, both Harry and William attended a rededication service at Diana's grave as 2017 marked 20 years since the Princess' tragic death. The Duchess of Cambridge and their children Prince George and Princess Charlotte also joined, and travelled to Althorp where Diana is buried. The private service was conducted by the Archbishop of Canterbury and attended by Diana's family.

The royal couple attended the charity game on Saturday, where Meghan cheered Harry as he played

GALLERY: Prince Harry and Meghan enjoy a night out with the Queen

Given the milestone anniversary of her death last year, William and Harry took part in two documentaries where they spoke fondly about their mother, and shared some of their favourite, as well as most painful, memories. It was the first, and possibly last, time the brothers spoke publicly and in depth about their mum.