The tiny top features an image of seven of the Queen's dogs, inspired by a painting by British artist Cindy Lass which was presented to the monarch on her 80th birthday.
The Queen is said to adore the portrait, which hangs in her private quarters in Buckingham Palace.
Knowing the Queen enjoyed the painting, Lass decided to reprint it onto a baby-sized T-shirt for George and was delighted when she received a note from Her Majesty thanking her for the "greatly appreciated" gift.
"When I got the letter back to say that Her Majesty had passed it on to him, it was very sweet," Lass told Hello! magazine.
"My mum saw the letter with the heading Buckingham Palace, saying it was going to be passed onto Prince George of Cambridge, and she said, 'Oh my God, the future King's going to be wearing one of your designs.' She was really proud. I felt her pride.
"The fact is, is that it made Her Majesty happy to give it to her great-grandson, so it's lovely to be part of that chain."