Queen Elizabeth’s youngest great-grandchild is “a little rockstar,” or at least, that’s how proud mom Princess Beatrice referred to her baby girl Sienna in a handwritten note. The thank you card from the 33-year-old Princess and her husband Edoardo Mapelli Mozzi was shared on Twitter Thursday by a royal fan.

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“How delightful. A lovely thank you from Princess Beatrice and Edo on their daughter Sienna Smiling face with 3 hearts #Royalreply #PrincessBeatrice,” the social media user tweeted.

The card featuring Sienna’s footprints reads: “Thank you so much for thinking of us at this remarkable and special time. We are so thankful to have welcomed this little person into our family. She is a little rockstar! With love, Beatrice, Edo, [Wolfie] and Sienna.”

Beatrice welcomed her daughter Sienna Elizabeth Mapelli Mozzi last September at London’s Chelsea and Westminster Hospital. The royal’s husband Edo is also a father to son Christopher Woolf, whom he shares with his ex Dara Huang.

The couple has yet to share a photo of their baby girl’s face, but did release a picture of Sienna’s footprints while announcing her name in October. Grandmother Sarah Ferguson has previously said that Sienna, who is eleventh in line to the throne, is “very, very beautiful.”