Princess Kate Middleton and Prince William – the new Prince and Princess of Wales stepped out on Saturday for their first outing together since receiving their new titles, accompanied by Prince Harry and Meghan Markle in a sweet surprise.

The foursome took an emotional tour of the tributes to the late Queen Elizabeth and greeted well-wishers at Windsor Castle for about 40 minutes. They all left in the same car, driven by William. According to Kensington Palace, Prince William invited his brother and sister-in-law to join him and Kate on the outing.

William thought the walkabout to greet the crowds "was an important show of unity at an incredibly difficult time for the family," a royal source says.

"It's such an extraordinary historical moment and also a deeply personal one for the family that you'd hope and think that all members of the family would unite and support [the King] especially. And perhaps some of those wounds can be healed in the process." someone in the crowd shared. 

The couples delighted the crowds of people, who have flocked to the castle since news of the Queen's death was announced on Thursday.