"Wishing a very happy birthday to The Duchess of Sussex today!" The caption read.
The royals’ message quickly drew up a response, with more than 500,000 people liking the pic and a number of fans left comments.
"The Cambridges are very kind," wrote person one, while another added: "The Cambridges, classy as always!'
Meanwhile, another royal fan wrote their own well wish to the Duchess, writing: "Happy Birthday beautiful lady. Keep being a force of change."
Prince Charles and Duchess Camilla also shared a sweet message for Meghan on her 39th birthday.
"Happy Birthday to The Duchess of Sussex! " the caption read.
For their choice of snap, Charles and Camilla picked a beautiful photo of Meghan from 2018, where the Duchess looks radiant in a navy knit.
Buckingham Palace also shared a candid snap from 2018, which shows Meghan and Her Majesty stepping out together in Chester.
"Wishing The Duchess of Sussex a very happy birthday!" The Queen's representative account added in the caption.
While Meghan and Harry are keeping their movements under the radar as they settle into life outside of their former senior roles, it’s likely the family-of-three had a celebration of their own on Tuesday.
Given their close proximity to Meghan's mother, LA-based Doria Ragland, it's also likely they joined her to mark the occasion.
In the coming weeks, we'll hopefully see some developments in the reveal of the couple's brand new charitable foundation, Archewell.
It's understood Harry and Meghan have been working hard behind the scenes to bring their new venture to life during the COVID-19 lockdown.
Stay tuned, these two are not unfamiliar with being quick to the punch, so we'll no doubt have more updates soon.