Pierre's mother Princess Caroline and Pierre's older siblings Andrea and Charlotte will also support the groom on the day.
Andrea's wife Tatiana Santo Domingo, who married in the palace two years ago, is expected to attend, but it is not yet known whether Charlotte's partner Gad Elmaleh can make the date.
On Pierre's side, his uncle Prince Albert, who is the reigning monarch of the small principality, and Albert's wife Princess Charlene will attend.
The prince will also give a speech to toast the newlyweds at the reception.
The space was designed by Albert's late mother Grace Kelly, who wanted to reflect American homes with outdoor areas.
The couple have asked for charitable donations as part of their wedding gifts The menu: Given the summer garden party theme, the menu will consist of picnic style food and light dishes.Princess Caroline's other daughter from her marriage to Prince Ernst, 16-year-old Princess Alexandra, is also expected to attend, as are Pierre's aunt Princess Stephanie and Stephanie's children Louis and Pauline Ducruet and Camillle Gottlieb.On the Borromeo side, members of the aristocratic Italian family will travel to Monaco, including the bride's parents Count Don Carlo Ferdinando Borromeo and Countess Donna Paola Marzotto.The reception: Prince Albert, who has played a part in the wedding preparations, is planning a "cavagnëtu", or in other words, a garden party, for his nephew and new bride.At the start of the reception, the monarch will give a speech before the alfresco party kicks off."Pierre had this [country-style] upbringing, which he loved," said an insider."He wanted to have a wedding reminiscent of his childhood and to share that with his bride." A heavy dose of glamour and elegance will also be thrown into the mix and the reception will reportedly be held in a part of the palace gardens that is rarely pictured – a covered terrace.Explaining the meaning of "cavagnëtu", Prince Albert said it was the "equivalent of a picnic"."Though we won't have submarine sandwiches or hamburgers or hot dogs," he joked to ."It's a light fete and I will give a toast," Albert told A garden party-style reception will follow, with 700 guests invited Sources added that Pierre wanted to hold a picnic-style celebration to reflect his upbringing in Provence.When his father Stefano Casiraghi died when Pierre was three, Princess Caroline raised her children in the French countryside.