In her book, The Other Side of the Coin, published in 2019, Ms Kelly, described how the replica gown was dyed in Yorkshire tea “(the strongest, as we all know)” to ensure it looked authentic.

She said: “At each stage of the process I would show our progress to the Queen: first the bodies, then the sleeves attached to it, then the skirt with the under-layers on, and finally the completed robe,” she wrote. 

“Her Majesty was very interested to see how it was developing.”

In the photograph, baby August can be seen wearing white clothing underneath the gown. 

His second cousin, Lucas, just seen in the background in his mother’s arms, appears to be wearing similar clothing, suggesting that each baby may have worn the gown as he was christened.

The original Spitalfields silk and Honiton lace gown was commissioned by Queen Victoria in 1841 for her first child, Victoria. 

The last royal baby to wear it was Lady Louise Windsor in April 2004, after which it was deemed too delicate to be used again so the Queen commissioned an exact replica.

Princess Eugenie and her husband, Jack Brooksbank, had their first child, August Philip Hawke Brooksbank, on Feb 9, while Mrs Tindall and her husband, Mike, welcomed their third child, Lucas Philip Tindall, on March 21.

Both boys share the same middle name, Philip, in tribute to their late great-grandfather the Duke of Edinburgh.