Royal sleuths were able to determine that the candid photo is actually from fall 2018

Kate Middleton and Prince William celebrated Mother’s Day in the U.K. with a glimpse into their personal family photo albums.

The couple shared a previously unseen photo on social media Sunday in honor of the holiday, showing Princess Charlotte and Kate sporting matching smiles as the little royal rides on her mom’s back. In the background, Prince George can be see enjoying a piggyback ride from dad William.

Royal sleuths know that the photo is actually from fall 2018, when the Cambridge family gathered for their annual Christmas card photo at their country home in Norfolk, Anmer Hall.

In addition to being taken by the same photographer — Matt Porteous, who also shot Prince Louis’ christening and some of Prince George‘s birthday portraits — Kate wears the same olive sweater over a collared shirt. Meanwhile, Princess Charlotte is wearing the same blue cardigan, which happens to be a hand-me-down from big brother George!

Kate Middleton

The photo session appears to be a favorite of Kate and William’s family. To celebrate Kate’s 38th birthday in January, they opted to release a new portrait — where the royal mom casually perches on a wooden fence — that also appears to be taken during the same set.

Catherine Duchess of Cambridge, new portrait released on her birthday
Kate Middleton’s 38th birthday portrait
| Credit: Matt Porteus/Kensington Palace

The Mothering Sunday tribute also included throwback photos of Kate’s mother, Carole Middleton, as well as William’s late mother Princess Diana. In the post’s second photo, Diana sits with her arm around Prince Harry as William gives his mother a hug around the neck.

The walk down memory lane also included a shot of Carole holding an infant Kate in her arms.

Grab Cut Insert Cut F:PHOTOMediaFactory ActionsRequests DropBox21239#retnacarrick0166625085.jpg
Prince Harry, Prince William and Princess Diana
| Credit: A.G. Carrick/Diana Memorial Fund/Getty
Carole Middleton
Carole Middleton and Kate Middleton
| Credit: Kensington Palace/ Instagram

To top off the personal post, the proud parents also included a photo of George’s sweet handmade card.

“To mothers new and old and families spending today together and apart – we are thinking of you all at this difficult time. Happy Mother’s Day 🌷,” the post read, acknowledging the difficult situation many families around the globe face due to the coronavirus pandemic.

Kate Middleton
Prince George’s Mother’s Day card
| Credit: The Duke and Duchess of Cambridge/ Kensington Palace/ Instagram

Can’t get enough of PEOPLE‘s Royals coverage? Sign up for our free Royals newsletter to get the latest updates on Kate Middleton, Meghan Markle and more!

On Thursday, Prince William and Kate showed their support for emergency workers who are helping to keep people well-informed about coronavirus by visiting a call center run by the London Ambulance Service.

Earlier this week, it was announced that George, 6, and Charlotte, 4 — who are enrolled at Thomas’s Battersea — will be continuing their lessons at home moving forward. The royal children will now move to “remote learning” and continue their lessons using online sources, their school said in a statement.