The collage included snaps from Harry's first day of school, teenage years and during his time in the army.
The touching post also featured a photo of baby Harry with his late mother Diana.
For his wife's birthday last month, Harry posted an equally touching message on Instagram.
"Happy Birthday to my amazing wife. Thank you for joining me on this adventure! — Love, H," he wrote.
While it hasn't been confirmed what Markle gifted her husband for his birthday, for her birthday last month he reportedly gave her a simple but sentimental present.
"The odds are on a sepia or black and white photograph of her precious son in a solid silver frame from Aspreys [a British luxury brand]," a royal source said last month.
"The precious present is likely to have an engraving chosen by Harry that will make it extra special.
