The Colombian beauty was pictured during a party, which took place in Princess Caroline's luxury yacht Pacha III. She was surrounded by her nearest and dearest, including sister-in-law-to-be Charlotte Casiraghi and her fashionista aunt Lauren Santo Domingo.
The bohemian theme, which saw all invitees wearing white dresses and gorgeous pink floral garlands, suited the bride's laid-back style to a tee. Andrea's younger sister Charlotte (pictured bottom left), who is thought to be in her second trimester, flattered her growing baby bump with a billowing white maxi dress.
Andrea's future wife stood out from her group in a crimson Missoni coloured dip-dye dress and cream-coloured flowers in her headpiece.
The 29-year-old heiress looked serene with the wind blowing softly through her long brunette locks as she posed for the photograph with an adorable pooch sat on her lap. Lucky invitees also included Noor Fares, Eugenie Niarchos, a Greek socialite and jewellery designer and Italian high flyer Bianca Brandolini.
Tatiana's Monaco wedding to her long-term love Andrea is likely to be an equally picture-perfect, star-studded affair.
Tatiana is best friends with Margherita and Teresa Missoni, who are both heirs of the hugely successful fashion empire Missoni. It is thought that the label may well be called upon to create her bridal gown.
Tatiana, who is a regular on the New York social scene, owns her own fashion company – in 2011 she launched the Muzungu Sisters fashion venture, which focuses on ethical business practices that allow them to support local craftsmen by buying handmade garments at a fair price and then selling them.
Their brand has been championed by other socialities, including Margherita, Eugenie Niarchos and Gaia Repossi.
A spokesperson has said that the affair will be 'private', although around 400 guests are expected.