The Prince of Wales and Duke of Sussex accompanied senior royals to march behind the Queen's coffin in an echo of their mother's funeral.
King Charles and other senior royals – including the Princess Royal, the Prince of Wales and the Earl of Wessex – were all wearing military uniform for the procession of the coffin from Westminster Hall to Westminster Abbey for her funeral service.
The Duke of York and the Duke of Sussex, who are no longer working royals, wore suits as they marched behind the carriage.
It is the second time William and Harry have accompanied their grandmother's coffin during the period of national mourning.
Following an emotional service in Westminster Abbey, the brothers retook their positions in a procession through central London as the Queen passed by Buckingham Palace for the final time.
The late Queen will be taken to Windsor Castle where she will be laid to rest in St George's Chapel alongside her husband the Duke of Edinburgh.
The event marked the fourth time since the Queen's death that Harry and William have been pictured carrying out an engagement together, sparking hopes they may be able to put the past behind them and rekindle their relationship.
The pair joined their six cousins to stand vigil at the Queen's coffin as she lay in state on Saturday, joining hundreds of thousands who queued to pay their respects to the late monarch.
Harry was granted permission to wear his Blues and Royals uniform for the vigil, having been told to wear a morning suit for the rest of the events to commemorate his grandmother.
The brothers also appeared at a walkabout with the Princess of Wales and Duchess of Sussex outside Windsor Castle two days after the Queen's death.
While the rift seems to have been put aside during the period of mourning, there are fears things could once again turn sour as Harry prepares to release his memoirs of time growing up inside the royal family.
The brothers have had a strained relationship since Prince Harry quit as a working royal and moved to California with his wife Meghan.
Since then, the pair have rarely been pictured in public together, but on Monday stood side-by-side as they walked with the Queen's coffin.
The event sparked memories of the brothers walking behind the coffin of their mother Diana, Princess of Wales, who was killed in a car crash in 1997.
The two princes, aged just 15 and 12 at the time, walked behind, in a moment which William later said was the "hardest thing" and was a "very long, lonely walk".
William said of walking behind his mother's funeral that not crying was an act of "self-preservation"
While viewing flower tributes to the Queen in Sandringham on Thursday, William reportedly chatted to an onlooker and told her the procession brought back memories of when he was a teenager.
Jane Wells, 54, from Lincolnshire, told the Telegraph: “He said how difficult it was yesterday and how it reminded him of his mum’s funeral... Catherine said it’s just been such a difficult time for all of them, for the whole family.”
He was also caught on camera talking to the public, was heard saying: "Doing the walk yesterday was challenging, it brought back a few memories.
"It's kind of one of those moments where you think to yourself 'I've prepared myself for this, but I'm not that prepared'."