William and Kate also tweeted out a photo of Meghan and wrote: “Wishing a happy 40th birthday to The Duchess of Sussex!”
Prince Charles and Camilla followed suit with a similar post: “Wishing The Duchess of Sussex a very happy 40th birthday.”
Princess Eugenie also paid tribute to Meghan on her special day, and took to her Instagram Stories to write: "To celebrate dear Meghan's 40th birthday I'm contributing 40 minutes of mentorship to support women reentering the workforce."
It comes after Meghan made a new video appearance via the Archewell site to launch a new initiative.
The 40x40 initiative encourages people to commit 40 minutes of their time to support women going back to work through mentorship or community service.
The announcement was made with comedian Melissa McCarthy over a video call, and Harry also made a surprise appearance.
As Meghan spoke with Melissa over video call, Harry could be seen at the end of the video in the window of the couple's mansion in California, as he appeared to attempt to juggle.
In the video, there was also a brief glimpse of the couple's newborn daughter Lilibet, where a picture frame on Meghan's desk seemingly featured family shots.
Meanwhile, the Duchess spoke with Melissa about the millions of women in the US and around the world who lost their jobs in the pandemic, and asked women to consider offering 40 minutes of their time to mentor someone back into the workplace.