A fan of the British royal family has shared a letter of thanks from the Duke and Duchess of Cambridge, which bears a previously unseen photo of Prince Louis, 2.
"Birthday reply from Prince Louis," the royal fan captioned the photo, which shows the card lying on top of its envelope.
The Instagram user, Katharina, from royal fan account Kat's Royal Letters, has been "collecting royal replies since 2015".
The note from the Cambridges reads: "The Duke and Duchess of Cambridge appreciated your kind thought in writing to Prince Louis as you did on the occasion of his second birthday.
"This was greatly appreciated by Their Royal Highnesses who send you their best wishes."
The photo was taken by the Duchess of Cambridge at Anmer Hall, the family's Norfolk home.
In the photo, Prince Louis is wearing the same blue and white chequered shirt he was wearing in the official images shared to mark his second birthday on April 23 this year.
The photo demonstrates a strong family resemblance, as in it, Prince Louis is the spitting image of his older brother, Prince George, 7.
Fans have been quick to point out how similar it is to a photo shared on George's fourth birthday in July 2017.
In both pictures, the brothers are wearing blue and white shirts, with the older of the two wearing stripes, not a chequered print.
Their swept hair and cheeky smiles, however, match perfectly.
On the same day, Kat's Royal Letters received a note of thanks for the wishes she sent to Princess Charlotte on her fifth birthday in May.
The almost-identical note reads: "The Duke and Duchess of Cambridge appreciated your kind thought in writing to Princess Charlotte as you did on the occasion of her fifth birthday."
It was printed on the back of one of the photos shared of the young princess on her birthday. Like the pictures of her brothers, it was taken at the family's home at Anmer Hall by mum, Kate, Duchess of Cambridge.
Kat's Royal Letters runs a blog, sharing images of correspondence received predominantly from the British royal family, but also from other notable European royals, including those in Sweden, Monaco, Belgium, Germany, Luxembourg and Spain.
On her Blogspot page, she has shared advice on how to best address the respective royal families and has listed their public addresses, where letters can be sent.
She has also explained which royal families are likely to respond, saying the Belgian and Monegasque royals are "great with replies".
However, those writing to the Swedes shouldn't hold their breath while waiting for a response. She says only Princess Sofia, Prince Carl Philip and Princess Madeleine write back, and even then it is "very rare".
On Instagram, the first reply she shared was from Prince Harry and Meghan, Duchess of Sussex, after their 2018 wedding. She has also posted and shared letters from Queen Elizabeth II, Prince Albert II of Monaco and Sweden's Princess Sofia.