Britain's Prince William, left, Prince Harry and Meghan Markle attend a Service of Thanksgiving and Commemoration on ANZAC Day at Westminster Abbey in London, Wednesday, April 25, 2018. (Eddie Mulholland/Pool via AP)

Prince Harry and Meghan Markle's will attend their first royal engagement as a married couple just three days after they tie the knot.

The flame-haired royal and the 'Suits' star will be attending the Prince of Wales' 70th Birthday Patronage Celebration on May 22, which take place in the gardens of Buckingham Palace.

The event will honour Prince Charles' patronage as well as his military affiliations too. Charities that he supports will be honoured as well as the emergency services who helped the victims of the Manchester Arena bombing, which took place a year ago this month.

Meanwhile, earlier this week, Harry and Meghan's wedding was given the official seal of approval from Queen Elizabeth. 

Read: Prince Harry, Meghan Markle's wedding receives Queen's seal of approval

The Instrument of Consent, a hand-written document that will be given to the loved-up couple after they tie the knot, read: "NOW KNOW YE that We have consented and do by these Presents signify Our Consent to the contracting of Matrimony between Our Most Dearly Beloved Grandson Prince Henry Charles Albert David of Wales, K.C.V.O., and Rachel Meghan Markle (sic)"

Harry and Meghan will tie the knot at St. George's Chapel, Windsor Castle on May 19.