This is Harry's first birthday since he stepped down as a senior member of the royal family in March. Harry and his wife, Meghan Markle, have since relocated to Santa Barbara, California, with their 1-year-old son, Archie.
ET spoke with royal expert Katie Nicholl about what the duke had planned for his special day, noting that it'll be a "low-key affair."
"Just on this occasion they celebrated quietly at home," Nicholl told ET. "I'm told they got the chance to switch off from their devices. They weren't actually working yesterday, so it would have been just a nice family day enjoyed with the three of them."
It's also likely that Harry will spend his actual birthday reconnecting with royal family members.
"He is going to have connected with his grandmother, [Queen Elizabeth], who I'm told he speaks with quite regularly," Nicholl shared. "The queen loves to see Archie and catch up on the family and their news. He would have also spoken to his father, the Prince of Wales, and I would be very surprised if there hadn't been a conversation with William and the Cambridges."