The singer-and-presenter is reportedly worried about the rugby player's plans to fly out to Las Vegas with several of his pals ahead of their forthcoming wedding, and is insisting they throw a joint pre-marital party for their friends.
A source told the Daily Star newspaper: "He called up all his old pals and said he wanted to spend five days in Vegas drinking and partying. Gav wants it to be the party everyone remembers. All his friends are really up for it and his dad, Alan, is coming along too.
"Charlotte knows what Gav's schoolmates are like and reckons things will get out of hand. She's worried they'll shave his eyebrows off or get him arrested for something silly like being naked in the street.
"Now she's trying to talk Gav into having a joint do so she can keep her eye on him."
The 24-year-old star and her 28-year-old fiance - who have two children, Ruby, two, and 15-month-old Dexter - are reportedly hoping to tie the knot on Paradise Island in the Bahamas in the summer.
A source said: "Gavin and Charlotte are planning to get married in July. Gavin picked Paradise Island in the Bahamas because he likes the idea of seeing Charlotte walking down the beach in a wedding dress.
"They're hoping to exchange vows on one of the island's stunning white beaches, then have a glitzy reception afterwards. It's the perfect place for a romantic wedding."