Click on photos below for gallery of Charlotte.
The French comedian has spoken for the first time about the beautiful Monegasque royal, and his excitement at welcoming the couple's first child together.
"Charlotte is very intelligent and has a great sense of humour," Gad told PEOPLE. "She's doing well and is so excited about becoming a mother.
"Charlotte will be the best mother in the world because she's generous and loving. She has all the right qualities to be a good mother.
"I'm a very happy man. I'm so lucky to be with her and I'm at a point in my life where building a family is very important."
Gad, 42, has been lovingly welcomed by Charlotte's family and it seems that the royal's mother, Princess Caroline of Monaco, has developed a soft spot for her daughter's boyfriend.
"Princess Caroline has a great sense of humour," said the comedian. "I think she likes my jokes. She laughs a lot. Charlotte has inherited her sense of humour. Her family are very kind and generous. They aren't intimidating at all."
While Gad and Charlotte, 27, were rumoured to be engaged, the on-screen heartthrob set the record straight.
"I can assure you we're not engaged," said Gad. "One day, perhaps, but for now we aren't. My mother rang me and said, 'I heard you're getting married on 14 September' and I said, 'What?'
"They were so surprised. But I can confirm, we haven't got married and we aren't engaged."
Gad, who already has a 12-year-old son Noé from his previous relationship with French actress Anne Brochet, also spoke about how he first met Charlotte in 2011.
"We don't have a crazy love story, nor a fairytale," admitted Gad. "The most beautiful stories are the ones that are real. The great thing is that we were friends before.
"When you know someone first as a friend, you get to know them and you talk a lot, and then you really understand who the other person is."