Sir Timothy is wearing a black suit paired with a white shirt and a maroon tie.
The card reads: “With Best Wishes for a Happy and Peaceful Christmas and New Year,” followed by Anne signing off the card in her own handwriting.
But fans quickly noted the fact that Sir Timothy did not add his signature to the card.
One user wrote on X, formerly Twitter, “Interestingly not signed by both of them”, while another one said: “Why is it that only her name appears…”
A third one explained: “These cards are sent to Anne’s patronages and charities, I think they send personal cards to friends and family where Tim signs them too [love heart emoji]”.
It comes as the royal couple are set to celebrate their 31st wedding anniversary on December 12.
The Princess Royal tied the knot to her second husband Sir Timothy in Balmoral on December 12, 1992.
