Prince Harry and Prince William's 'Awkward' Outing After Queen's Death: 'Both Couples Found It Hard'

Prince William and Prince Harry's show of unity outside Windsor Castle after Queen Elizabeth's death was a surprise for many — and it was not easy for the

brothers. "It was awkward. Both couples found it hard," an insider tells PEOPLE in this week's issue of William, his wife Kate Middleton, Harry and his wife Meghan Markle.

"They were in a stoic spirit of just getting through it for the Queen." The outing on September 10 came two days after William and Harry's grandmother Queen Elizabeth died

at age 96 at Balmoral Castle in Scotland. Along with Kate and Meghan, Prince William and Prince Harry stepped out together for a walkabout, greeting well-wishers and taking

in the flowers and other memorial items left for the late monarch. Kensington Palace said at the time that William invited Harry and Meghan to join him and Kate. Another

source added that security was not expecting both couples. RELATED: How the Royal Family Came Together amid Tensions to Honor Queen Elizabeth: 'Everyone Was Hurting'

Prince 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 previously told

PEOPLE. Added a palace insider, "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 [King Charles III] especially. And perhaps some of those wounds can be healed in the process." The reunion among the foursome was

poignant, as relations have been strained the Duke, 38, and Duchess, 41, of Sussex and members of the royal family in recent years.