It has been revealed that the bride's father, Formula 1 tycoon Bernie Ecclestone, has spent upwards of £1.3 million to create the wedding of his 22-year-old daughter's dreams.
The socialite is the youngest of his two girls with his ex Slavica, a former Armani model from Croatia, whom he was married to for 25 years until their divorce in 2009.
James, a businessman, who is thought to be 28, popped the question after a four-year courtship. The young lovers celebrated their engagement earlier this summer with the party of a lifetime.
And bride-to-be Petra had enlisted none other than Rihanna to perform for their guests.
Shortly afterwards, at James' suggestion, the pair signed a complex pre-nuptial agreement, in which both of their assets would be protected in case of a future split.
Castello Odescalchi, an imposing castle, which was built in the15th century just outside Rome, will host the sumptuous reception when they tie the knot on August 27.
Overlooking the southern shore of Lake Bracciano, the mansion has been frequented by popes, kings and aristocracy throughout its history.
In recent years, the bluebloods and statesmen have given way to celebrities like Tom Cruise and Katie Holmes who became man and wife there in 2006.
Bernie is reported to have spent £310,000 to secure the exclusive venue and accomodation for all the lucky guests, who include Princesses Beatrice and Eugenie.
Odescalchi has also agreed to put on a £40,000 fireworks display at the end of the evening.
The star-studded reception:
When Rihanna serenaded the couple in honour of their engagement, the F1 chief set the bar high for the wedding itself.
The billionaire certainly will not disappoint – both Eric Clapton and The Black Eyed Peas have been booked for the rocking post-nuptials party.
Eric, who rarely performs live, is a close friend of the family and will play as Petra and James share their first dance.
A friend of the bride has said: 'Petra is Bernies little girl. He'll do anything to make her happy and she wants a wedding to leave her society chums green with envy...[she] had her heart set on Fergie and the Black Eyed Peas and used her connections."
The couple's new home:
While Petra owns a £56-million home in Chelsea, she recently revealed she would like to move to Los Angeles after buying America's most expensive house.
The 'nearlywed' spent £85-million on the former home of TV mogul Aaron Spelling – equipped with 193 rooms, a tennis court and pool.
Petra hopes to relocate to California where she can pursue a career in handbag design and begin her life with James.