According to UK Daily Mail, the child would not stop crying during the ceremony; causing the clergyman to lose his temper, lift his left hand and hit the baby in the face.
Suddenly, the priest appears unable to take it again and deals the hollering baby a quick slap in the face.
A couple presumed to be the parents is heard gasping at this in the video. "I will scream louder than you so calm down".
The outraged relatives then stepped in and snatched the baby away from the priest, after watching on in shock.
The priest, who is speaking French, is seen blessing the baby and the child begins crying.
Eventually, the priest grabs the baby by the chin and delivers a firm slap across the baby's face.
The disturbing video has been circulated on social media, but it is still unclear where it was filmed. "Slap. My Child. Imma show you that these hands can do more than show you that I'm praying [sic]".
Kensington Palace has officially announced the date of Prince Louis' christening
Meghan made her Royal Ascot debut yesterday without Kate to lean on for support, but on the arm of her new husband Prince Harry . Kensington Palace confirmed: " Prince Louis will be christened by The Archbishop of Canterbury, the Most Reverend Justin Welby".
"The way he was holding the child was already a warning sign".
"I wonder how many millions of kids suffer inappropriately aged "discipline" like this behind the scenes in religious families who believe this is biblically sanctioned, though", One woman wrote.
The video shows the man vigorously dunking the small child into the water before being handed back to seemingly unperturbed parents.
Unbelievably, there were some commenters who defended the priest's actions.
Internet users are confused, anxious and appalled at the priest's actions, with one person writing, "That was uncalled for".
The congregation gasps and admonishes him for his treatment of the child.