Her partner French actor and stand up comedian Gad Elmaleh wound up his international tour by giving his final performance in Monte Carlo's Salle De Princes on 13 December.
This was undoubtedly organised to allow the 42-year-old to be on standby should his girlfriend of two years go into labour. He isn't due to return to work until 8 January.
According to the Nice Matin newspaper, Charlotte, 27, is booked into the Princess Grace hospital, where she and her two brothers were born.
Anticipation is high in Monaco for the birth of Caroline's second grandchild - her first Sacha, who is the son of Charlotte's eldest brother Andrea and his wife Tatiana Santo Domingo arrived in March.
But Charlotte has always been a particular favourite locally because of her striking looks and uncanny resemblance to her mother.
No word yet on the sex of the baby - the family has released no information on the pregnancy. The mum-to-be likes to guard her privacy, insisting she isn't a Princess "only the niece of a head of state" (Prince Albert).
Gad, who has a 12-year-old son from a previous relationship, has been more forthcoming, saying it iss a time of "joy and excitement" and that he is at the point in his life when "building a family is very important".
He added: "Charlotte will be best mother in the world because she is generous and very loving. She has all the gifts for being a mother . She's precious and very loving and kind."