The Duke and Duchess of Sussex held a closed-door christening Saturday morning for baby Archie in the Private Chapel at Windsor Castle, where only about 25 people were reportedly in attendance for the intimate ceremony. They snapped this pic afterward.

It's the whole family here pretty much -- sans Queen Elizabeth and Prince Philip -- with Meghan and Harry front and center, and Archie on mommy's lap.

Check out the mug on the baby BTW -- it's the first time we're seeing the kid's face in full view since he was born, and lo and behold ... the 2-month-old is absolutely adorable.

As for other details, the Royals have been pretty tight-lipped -- only saying in their announcement, "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."

A rep added, "Their Royal Highnesses feel fortunate to have enjoyed this day with family and the godparents of Archie." No word on ID of godfather -- keepin' it in the family, it seems.

And, if you were wondering about the christening wear of the child, the Royals explained that too, saying it's actually a replica of a traditional gown that's been worn by royal infants for 11 years. Of course, the Royals are all about tradition ... in religion and otherwise.

One last fun fact -- the guy who handled Archie's christening -- Archbishop of Canterbury, Justin Welby -- is the same dude who baptized Meg before she got hitched with Harry. She was already raised Christian, but it never hurts to make things official.