Royal sisters-in-law Meghan Markle and Kate Middleton reunited this week for the first time publicly since Christmas.

Markle, the Duchess of Sussex, and Middleton, the Duchess of Cambridge, attended a reception at Buckingham Palace Tuesday. The event, which was hosted by Queen Elizabeth, marked the fiftieth anniversary of the investiture of the Prince of Wales, the Daily Mail reported. The two women were accompanied by their respective husbands, Prince Harry, 34, and Prince William, 36.

Britain's Kate, Duchess of Cambridge attends a reception at Buckingham Palace, London, Tuesday March 5, 2019, to mark the fiftieth anniversary of the investiture of the Prince of Wales. (AP)

Markle, 37, wore what People described as a “metallic brocade knee-length dress,” while Middleton, 37, donned a mint-green, high-necked ruffled dress.

Christmas Day in Sandringham was the last time the two royals were seen together publically, the magazine reported.

Though Charles, 70, was “created the Prince of Wales” in July of 1958 when he was 9 years old, he wasn’t “formally invested with the title by Her Majesty” until July of 1969, according to the Clarence House. Prince Charles’ wife, Camilla, the Duchess of Cornwall, was also at the event.

Meghan Markle, Duchess of Sussex, also attended the event with her husband Price Harry. (AP)

Prime Minister Theresa May attended the party, as did the Archbishop of Canterbury Justin Welby. Welsh Secretary Alun Cairns, who reportedly congratulated Markle on her soon-to-be-born child, was also in attendance.

“'I look rather different than the last time you saw me', she joked in response, according to the Daily Mail.

“Yes it's sweet, we're nearly there,” she added.

Kate Middleton stunned in a mint-green ruffled dress. (AP)

The event came just a day after the British royal family issued guidelines for its social media channels in the wake of the online abuse against Middleton and Markle, which has prompted concern in recent months.

The family said the guidelines have been put in place to “help create a safe environment on all social media channels,” which include the Royal Family, Clarence House and Kensington Palace. Users who post obscene or offensive content on the social media pages will be blocked or reported to police, the palace warned.

Fox News' Katherine Lam contributed to this report.