Tatiana, 31, and her husband Andrea – who is Princess Caroline of Monaco's eldest son – are already parents to two-year-old Alexandre, nicknamed Sasha.
A statement released by the principality on Tuesday confirmed the birth, expressing that both Tatiana and Andrea's mothers were thrilled.
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Tatiana Santo Domingo gave birth to a baby girl on Sunday
"Her Royal Highness the Princess of Hanover and Mrs Vera Santo Domingo are delighted to announce the birth of their granddaughter, born on 12 April 2015," the note read. "Mother and baby are doing well."
Not much else is known about the young tot, who has now become seventh-in-line to the Monegasque throne.
Her mum Tatiana did not formally announce her pregnancy. HELLO! Online's sister publication HOLA! exclusively confirmed that the New York-born beauty gave birth in London last week.
Tatiana and Andrea, 30, married in a civil wedding service in Monaco in August 2013 – just five months after Tatiana welcomed her first-born Sasha, also in London.
Tatiana Santo Domingo and Andrea Casiraghi are already parents to two-year-old son Sasha
The couple continued their wedding celebrations in early 2014, when they married again in a romantic church service in Gstaad, Switzerland. Members of Monaco's royal family were present including Princess Caroline, Prince Albert and the groom's siblings Charlotte Casiraghi, Pierre Casiraghi and Princess Alexandra of Hanover.
Tatiana was recently ranked the 847th richest person in the world, according to Forbes. With an estimated net worth of £1.4billion, Tatiana's main source of income comes from her inheritance of her grandfather's beer business.
Julio Mario Santo Domingo owned Colombian brewery Bavaria before trading it for 15 per cent of SABMiller in 2005. When he died six years later, he left one-sixth of his inheritance to Tatiana and an equal amount to her billionaire brother Julio Mario Santo Domingo III, who is a DJ in New York.
Known in the fashion industry for her boho-chic style, philanthropist Tatiana is also one half of ethical clothing and accessories brand Muzungu Sisters.