He has been in the UK for a week, which included isolating for five days at Frogmore Cottage before yesterday’s official unveiling of the new Princess Diana statue at Kensington Palace.
Harry travelled over from California without wife Meghan Markle, with the duchess having given birth to the couple’s second child, Lilibet, last month.
It appeared Harry and William had put aside their differences to honour their late mum and even shared a glass of bubbly after the event at around 2.45pm.
Harry, who along with Meghan stepped down as a senior royal more than a year ago, appeared in high spirits during the ceremony, which saw him reunited with a number members of his family from his mother’s side.
He and William, who have long reported to have a fractured relationship, chatted and joked together throughout.
The Sussexes’ relationship with the Firm itself was damaged significantly by a number of interviews conducted by Harry and Meghan in which they criticised royal life, starting with their Oprah Winfrey chat in March.
However, it appeared the brothers may have taken further steps towards overcoming their problems with each other during the unveiling.
After the ceremony, the princes released a joint statement that said they “wish” Diana “was still with us” and that they hoped the monument – commissioned by them in 2017 – would be seen as a “symbol of her life and her legacy”.
After testing negative for Covid-19, Harry was able to leave quarantine on Wednesday before surprising a group of inspirational children at an awards do.
In his first UK engagement since quitting the royal family last March, the Duke made a special visit to the WellChild awards in Kew Gardens, west London for a private garden party.
He said he felt “more connected, inspired and in awe” of the children since becoming a dad himself.
Harry, who has had a long association with the charity, was joined by celebrities including Ed Sheeran, Ronnie Wood, Amanda Holden, AJ Pritchard and Abbie Quinnen.
It is only the second trip back to the UK Harry has made since stepping down from senior royal duties – in large part due to the difficulty of travel amid the ongoing pandemic.
The first came in April when he attended grandfather Prince Philip’s funeral at Windsor Castle.