The image, taken in 1997, shows the future Duchess with her boyfriend at just sixteen.
She wears a slinky black dress with a choker, and her hair in an up-do, similar to the style she regularly sports on official engagements these days.
The young couple can be seen beaming as they stand in front of a Christmas tree.
The caption, accompanying the picture online, reads: “16 year old Meghan Markle [poses] with her first boyfriend Luis Segura at a high school Christmas dance in 1997".
Since being shared, the post has received more than 63,000 likes - and many social media users were amazed at how little the Duchess appears to have aged.