July 10, 2018 08:49 AM

Charlotte Casiraghi and her fiancé Dimitri Rassam are expecting a baby.

After weeks of press speculation, Casiraghi, 31, unveiled her bump during the recent Monte Carlo International Horse Jumping events. The news comes a few months after Princess Caroline of Monaco’s eldest daughter confirmed her engagement to Rassam by wearing a diamond ring on her left hand as they attended their first official Monaco event together in March.

A source tells PEOPLE that Casiraghi is “due late this summer, early September.”

The child will be the seventh grandchild for Princess Caroline (the 62-year-old royal’s clan has welcomed two additions since April) and the second grandchild for Dimitri’s mother, glamorous French actress and former Bond girl (For Your Eyes Only) Carole Bouquet.

Charlotte Casiraghi on June 30
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Charlotte Casiraghi and Prince Albert of Monaco
fotopress/Getty

Casiraghi and Rassam got engaged in March while on ski vacation in Zurs, Austria, with Princess Caroline. Their wedding plans remain secretive. Initially, it was speculated that they might marry as early as this month.

While an early October date has now been mentioned around Monaco, a source tells PEOPLE that plans now suggest a civil ceremony in December (their second anniversary as a couple), with a larger family wedding, similar to the glamorous 2015 ceremony of Beatrice Borromeo and Charlotte’s younger brother Pierre, scheduled for next spring.

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That event, sources indicate will be held in privacy at Bouquet’s 12-acre vineyard on the Italian island of Pantelleria.

Charlotte, who is ninth in line to Monaco’s throne, and the 36-year-old film producer (his credits include Netflix’s The Little Prince) quietly began seeing each other in Dec. 2016 after being introduced by friends over dinner.

Dimitri Rassam and Charlotte Casiraghi on March 24
Pascal Le Segretain/Getty Images

The eldest granddaughter of Grace Kelly and the film producer, who have been inseparable since, split their time between L.A., Paris and Monaco. Both are graduates of the Sorbonne University in Paris, and each have children from previous relationships: Charlotte has a 4-year old son, Raphael, with comedian Gad Elmaleh, and Dimitri has a daughter from his marriage to model Masha Novoselova.

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Philadelphia-born Grace Kelly became Princess Grace when she wed Prince Rainier of Monaco in 1956. When Grace — an Oscar-winning superstar who left her acting career after becoming a royal — returned to Philadelphia as a royal mom, the home continued to be a joyful refuge.

Grace Kelly on her wedding day
Michael Calcagno

“She seemed to have a very happy childhood, and it was a lot of games, a lot of fun things that were happening there,” Prince Albert, who recently unveiled the new restoration of his late mother’s childhood home, told PEOPLE, “and it felt like a real family home. It was a real place of gathering and rejoicing.”

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