"Happy Holidays," the card, that was first shared by non-government organisation Team Rubicon, read.
"This year, 2021, we welcomed our daughter, Lilibet, to the world. Archie made us a 'Mama' and a 'Papa', and Lili made us a family,"
"As we look forward to 2022, we have made donations on your behalf to several organisations that honour and protect families – from those being relocated from Afghanistan, to American families in need of paid parental leave."
Photographer Alexi reposted the photo to his own account and admitted on Instagram: "This is one of those rare and special projects, that one is fortunate enough to be a part of.
"To be able to continue the story of this family whom I first photographed as an engaged couple, then on the day of their wedding, as a married couple and now seeing their love manifest into two beautiful children, has been a delightful honour."
Alexi added that one of the "greatest joys" he receives from photography is when he's "able to photograph 'love' in some form or another."
"This day with the Duke and Duchess of Sussex was one such joyous experience, and one that I feel extremely privileged to have been invited to capture."
This story originally appeared on our sister site, Now To Love.