Meghan Markle attends polo match to cheer on Prince Harry

— -- Prince Harry was joined by his American girlfriend Meghan Markle at a charity polo match today, a significant step in the couple's relationship and the first time they have attended a public event together as a couple.

Markle stood on the sidelines cheering on the fifth in line to the throne while he rode at the Coworth Park Polo Club in Berkshire, England, to support his charity Sentebale. Harry was joined by his brother Prince William to raise funds and awareness for their various charities.

"Their Royal Highnesses have taken part in polo fixtures in support of their charities since 2007 and have continued each year since, raising over £10 million ($13 million) for charitable causes to date," Kensington Palace said in a statement today.

A slew of A-list celebrities including Eddie Redmayne and his wife Hannah Bagshawe, "The Crown" actor Matt Smith, and actor Tom Hardy were on hand to see the two princes play for their teams.

Markle has started to attend a number of high profile private events with Prince Harry. In March she accompanied him to a wedding in Jamaica for a childhood pal from Eton, the school Harry attended as a teenager.

Harry joined the "Suits" actress over Easter instead of spending Easter at Windsor with his family, indicating just how serious the relationship has become.

Markle is expected as Harry's plus-one at Pippa Middleton's wedding to Financier James Matthews in two weeks. She reportedly will not attend the church service but will attend the reception with Harry.

The couple met last summer when they were introduced by mutual friends and were photographed together for the first time last November attending a play and leaving the private Members Club Soho in February holding hands.

Markle and Harry have been nearly inseparable, with the two jetting back and forth across the Atlantic to spend time together. Recently Markle has spent weeks at Harry's Nottingham Cottage, and speculation has been rife that an engagement is likely in the coming months. The couple also took a romantic vacation together after the New Year to view the northern lights in Norway.

Kensington Palace announced that Prince Harry will be making an overseas tour to Singapore and Sydney in June to launch the 2018 Invictus Games in Australia, the international sporting competition for wounded, injured and sick servicemen and women founded by the prince in 2014. This fall, Harry's Invictus Games will be held in Toronto, where Markle films her television show "Suits."