"This morning, The Duke and Duchess of Sussex’s son, Archie Harrison Mountbatten-Windsor was christened in the Private Chapel at Windsor Castle at an intimate service officiated by the Archbishop of Canterbury, Justin Welby," the caption read.
"The Duke and Duchess of Sussex are so happy to share the joy of this day with members of the public who have been incredibly supportive since the birth of their son. They thank you for your kindness in welcoming their first born and celebrating this special moment."
"Their Royal Highnesses feel fortunate to have enjoyed this day with family and the godparents of Archie."
Archie's godparents haven't been named, however that Instagram caption would suggest that they were among those who attended the christening.
The small guest list included just four members of the Royal Family: the Prince of Wales and Duchess of Cornwall, and Duke and Duchess of Cambridge. The Queen and Duke of Edinburgh had a prior engagement.
Meghan's mother, Doria Ragland was there, alongside the late Diana, Princess of Wales' sisters, Lady Jane Fellowes and Lady Sarah McCorquodale.