Prince George and Princess Charlotte don't follow the traditional of addressing their grandmothers.

In an ITV documentary, "Our Queen at Ninety," Kate Middleton revealed that Prince George uses a different nickname when calling the monarch. "He calls her 'Gan-Gan,'" the Duchess of Cambridge said (via Good Housekeeping).

Middleton also shared that Her Majesty is a sweet and thoughtful great-grandmother. "She always leaves a little gift or something in their room when we go and stay, and that just shows her love for the family," the Duchess of Cambridge added.

Meanwhile, it remains unknown how Prince William and Middleton's kids address Prince Charles' second wife, Camilla Parker Bowles. The Duchess of Cornwall already has five grandchildren from her two kids with ex-husband Andrew Parker Bowles. Tom Parker Bowles has two while Laura Lopes has three children.

In 2013 after Prince George's birth, the Camilla was asked how she would like to be addressed by the new royal. She said the family hasn't decided for certain. However, she revealed that her grandkids call her "GaGa."

"I don't know if it's because they think I am," Camilla joked. "But it is still very sweet." Meanwhile, Prince Charles prefers to be called "grandpa" instead of "granddad."

In related news, the royal family is set to welcome a new baby soon as Middleton is set to deliver her third baby with Prince William this month. According to an insider, Princess Charlotte is already excited to be a big sister.

"William and Kate like to keep Charlotte involved and part of the excitement around having a new sibling," an insider said. "She's very aware she's going to have a new baby brother or sister."

The source added that the little princess plays with her dolls and pretends that they are babies. "So I think she is probably expecting the new brother or sister will be the same game — but in real life," the insider added.

St. Mary's Hospital is already prepping for the arrival of the newest royal baby. In fact, last month they have repainted the railings outside the Lindo Wing.

In addition, earlier this week, they placed a "No Parking" sign in the same area. The facility did the same two weeks before Middleton delivered Prince George and Princess Charlotte in 2013 and 2015, respectively.