Princess Caroline of Monaco has become a grandmother after Andrea Casiraghi’s fiancée, Colombian heiress Tatiana Santo Domingo gave birth to a baby boy on Thursday.

The family are yet to announce the newborn’s name.

Andrea Casiraghi, 28, is the oldest son of Princess Caroline and the nephew of Monaco’s ruling sovereign, Prince Albert II.

Prince Albert II is the son of late actress Grace Kelly and Prince Rainier III of Monaco.

The Monaco palace said Princess Caroline is overjoyed by the newest addition to the jet set royal family.

According to Hello magazine, the new baby will be third in line to the Monaco throne, behind Andrea Casiraghi (who currently has no title) and Princess Caroline, who is first.

This line of succession would change if reigning monarch Prince Albert and his wife Charlene were to welcome a child before Andrea Casiraghi and Tatiana Santo Domingo marry.

A royal birth is usually greeted with fanfare in Monaco, and will certainly be baptized.

Andrea Casiraghi has become a father after Tatiana Santo Domingo gave birth to a baby boy

Andrea Casiraghi’s sister, Charlotte has been tipped to be godmother.

The fact that Andrea Casiraghi and Tatiana Santo Domingo, 29, were expecting was never officially announced, though rumors were confirmed in November when Tatiana was spotted with a sizeable bump.

Tatiana Santo Domingo and Andrea Casiraghi, who announced their engagement in July last year, are relatively publicity-shy.

Andrea Casiraghi’s fiancée is the daughter of the late Julio Santo Domingo, named by Forbes in 2011 as the second richest man in Colombia, and Vera Rechulski, a former Brazilian socialite from Sao Paolo currently living in Paris.

They have known each other for eight years and met while studying at the same school in Paris.

No date has been fixed for the royal wedding but it is understood it will take place this year.

Andrea Casiraghi is the son of the late Stefano Casiraghi, the second husband of Princess Caroline, who died in a boating accident off Monte Carlo in 1990.