Meghan posted a candid image on the @SussexRoyal Instagram account, of her holding her baby boy in her arms, wrapped in a shawl, showing just his feet and her hands holding them.
Believed to have been taken within the grounds of their new home Frogmore Cottage in Windsor, it also features Princess Diana’s favourite forget-me-nots flowers in the background.
Meghan’s bridal bouquet for her wedding last May also included the same flowers, in another sweet tribute to Harry’s late mother.
The Instagram caption reads: “Paying tribute to all mothers today - past, present, mothers-to-be, and those lost but forever remembered.We honor and celebrate each and every one of you.
“Today is Mother’s Day in the United States, Canada, Australia, New Zealand, South Africa, Kenya, Japan, and several countries across Europe.
“This is the first Mother’s Day for The Duchess of Sussex.”
The post also included a quote from a poem called “Lands” by Nayyirah Waheed.
“My mother was my first country; the first place I ever lived.”
Meghan, 37, gave birth to son Archie Harrison Mountbatten Windsor at 05:26 on May 6, 2019 with husband Harry, 34, by her side.
The couple set up their own Instagram page on April 2, and it broke a world record by gaining one million followers within the first six hours of its launch.
At the time, royal watchers predicted that the first image of Baby Sussex would appear on social media.
Buckingham Palace announced the couple wanted to keep details around the birth of their first child private so they could enjoy some time with their newborn before showing him off to the world during a brief photo call last Wednesday.
But like any modern couple, they shared the news that their baby was a boy on their social media channel.
The traditional birth notice was also placed on the ceremonial easel outside Buckingham Palace on the day of his birth.
The couple’s immediate families were informed and Meghan’s mother Doria Ragland is “overjoyed by the birth of her first grandchild.”
Ms Ragland has been staying with her daughter Meghan and Harry at Frogmore Cottage in Windsor.
After the photocall on Wednesday, Harry and Meghan shared another photo of them with Archie, Doria and the Queen and the Duke of Edinburgh.
Archie is seventh in line to throne and is the Queen’s eighth great-grandchild.
The duke and duchess moved into their new home Frogmore Cottage at the beginning of April. They previously lived at Nottingham Cottage within the grounds of Kensington Palace.
Harry broke his paternity leave last Thursday to visit The Hague in the Netherlands to launch the countdown to the 2020 Invictus Games.
He also has a day of engagements in Oxford on Tuesday 14 May.