Fresh from Prince Louis's christening yesterday, the royal foursome arrived at the iconic landmark for a service celebrating the RAF's history.
Tomorrow, Meghan and Harry join the Royal Family for a service commemorating the centenary of the Royal Air Force before jetting off on a two-day visit to Ireland.
Also attending were Kate's parents, her brother and sister and Louis' six godparents, who are close friends or relatives of William and Kate.
The list includes: Mr. Nicholas van Cutsem, Mr. Guy Pelly, Mr. Harry Aubrey-Fletcher, The Lady Laura Meade, Mrs. Robert Carter, and Miss Lucy Middleton.
The group walked into the Abbey altogether and spoke with the Archbishop of Canterbury, who just a day earlier had Christened Prince Louis.
Harry and Meghan Duchess of Sussex leave after the christening service.
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There's not much to choose between the two sides: both have superb goalkeepers, strong defences and attacking talent in abundance. Marouane Fellaini, who has oft-partnered Pogba in the United midfield, will now be looking to stop the powerful Frenchman.
At her first royal christening, the former "Suits" actress gave a nod to her USA roots by wearing an olive-toned design by popular American designer Ralph Lauren.
The Duchess of Sussex wore a a black dress which featured a batueu neckline and a full A line skirt.
So although Kate Middleton has opted for a pale eggshell outfit, Meghan hasn't broken protocol by wearing an all-black outfit to this event.
The Queen looked well after skipping Prince Louis's Christening on Monday, following a busy week in Scotland last week.