A glittering treasure, covered in diamonds and commissioned for a dying dynasty.

This is the Winter Egg, made by legendary jeweller Fabergé and gifted by Russia's last Emperor Nicholas II to his mother, Dowager Empress Maria Feodorovna, on Easter Day 1913.

The imperial ruling family met a gruesome end, executed by the Bolsheviks in 1918. But some of their famous eggs survive.

This one will be auctioned next week.

Christie’s Fabergé expert, Margo Oganesian, says it is a particularly fine example.

“The Winter Egg is made of rock crystal. The egg itself and the base are cut from rock crystal. It would have been an extremely difficult job, first of all to find such a clear specimen of rock crystal, but then also carve it in such a difficult shape, the ovoid shape, and also engrave with the beautiful snowflake design from the inside without the rock crystal cracking. It must have been a really, really challenging job. And of course in 1913, before all the technology that we have now, this this was all made by hand of course,” she says.

“The egg and the base are applied with platinum mounts, very delicate platinum mounts looking like snowflakes, in the shape of snowflakes, and set with rose cut diamonds,” Oganesian adds.

“I didn't count them myself, but we have the original invoice from Fabergé, and he lists the number: 4,500 diamonds on the Winter Egg, which is astonishing.”

The Emperor commissioned two eggs every Easter - one for his wife and one for his mother.

They took an entire year to design and craft and came at huge expense.

"We know exactly how much it cost. The price was 24,600 rubles. It was the most expensive item of Fabergé created at the time in 1913. And just for comparison to understand how much money it was, an average worker in Moscow would get 30 rubles a month. So this was an incredibly high amount, ones that only Romanovs could afford, of course,” says Oganesian.

"And so the Winter Egg set the world record twice before when we sold it in 1994 and 2002. And on Tuesday we are going to offer it for sale again, and we expect it to sell in excess of 20 million pounds.”

Fifty Imperial Easter Eggs were created by Fabergé, but only 43 have survived.

This is the first time in more than two decades one has been available on the public market.

"There are only six other Imperial Easter eggs left in private hands, in private collections, and the Winter Egg is arguably one of the best imperial Easter eggs Fabergé ever created. The design of it, the craftsmanship, the story, the fact that it's complete with its surprise and the surprise wasn't lost like was the case with many other eggs, it all makes it incredibly important and rare,” says Oganesian.

The Winter Egg will be auctioned by Christie’s on 2 December in London.

AP video shot by: Cassandra Allwood