Catherine, Duchess of Cambridge tweeted a rare reply to a well-wisher as she celebrated her 40th birthday at the weekend.
The British royal celebrated the milestone birthday on Sunday (09.01.22) and sent a social media response to six-year-old Mila Sneddon as the pair have forged a special bond.
The video message was shared on social media by Mila's mother Lynda as the child sent her best wishes to the Duchess on her special day.
Mila said: "Happy Birthday Catherine! I'm so happy you're turning 40, hope you get nice gifts and love spending time with your family. Bye, lots of love, Mila."
In a surprise move, a tweet from Catherine and her husband Prince William's official account responded to Mila, saying: "Thank you Mila!"
Mila featured in Catherine's 'Hold Still: A Portrait of Our Nation' photography project which documented the nation during the coronavirus lockdown.
She was pictured kissing her dad through a window as she underwent intensive chemotherapy for leukaemia and had to shield during the height of the global health crisis as the image left a lasting impression on the Duchess.
The pair met in person at the Palace of Holyroodhouse last year and Catherine wore a pink dress after Mila revealed that it was her favourite colour.
As she walked into the room, Catherine said: "Hi Mila, look at you. I want to give you a big, squeezy cuddle. It's so nice to meet you in person."
The royal kept a promise she had made to Mila when they first spoke on the phone the previous autumn after learning about her passion for pink.
She said at the time: "I'll have to make sure I try and find a pink dress. Hopefully when, one day, hopefully, Mila, we'll get to meet and then I'll wear remember to wear my pink dress for you."