But some fans were disappointed with the snap, with one commenting:
“Why waste time photo the back [sic], it could be anyone.”
And another wrote: “Happy birthday! When will we see her face?”
Others were thrilled to catch a glimpse of the tiny royal, commenting on her little feet and her hat.
Born on September 18, 2021, just over a year after her parents were married in a low key ceremony due to Covid-19 restrictions, Sienna’s name has special meanings for the family.
The princess is understood to have chosen a name starting with “S” as a nod to her mother Sarah Ferguson and also to acknowledge the colour of the child’s hair being like her mother and grandmother’s.
A source told Hello! magazine: “They were looking for an Italian name which started with an S for Sarah, to honour the Duchess, and also reflected the golden rust colour of both the Duchess’ hair colour and Beatrice’s which the new baby shares.”
The inspiration for the child’s middle name, Elizabeth, will come as no surprise to royalists: chosen as a tribute to Beatrice’s late grandmother, Queen Elizabeth.
Sienna is 10th in line to the British throne, after her mother.