The pair were seen leaving the service at Windsor Castle together along with the Duchess of Cambridge.
There has been limited contact between the brothers since Harry and his wife Meghan filmed a tell-all interview with Oprah Winfrey last month.
Harry had referenced reports that his relationship with his brother was strained, saying “the relationship is space at the moment” and that “time heals all things, hopefully”.
In 2019, when asked about an alleged rift with William, Harry said he loved his brother dearly but they were “on different paths” and have “good days” and “bad days”.
The Duchess of Sussex, who is pregnant with the couple’s second child, did not fly over from the US with Harry on the medical advice of her doctor.
Prince Harry has since been self-isolating at Frogmore Cottage after arriving back in the UK.