Arnold Schwarzenegger Does Not Know the Sex of Katherine and Chris Pratt's Baby: 'I Can't Shut My Mouth'

If Katherine Schwarzenegger and Chris Pratt know the sex of their second child, they haven't told Arnold Schwarzenegger.

When it comes to the sex of Katherine Schwarzenegger and Chris Pratt's second child together, mum's the word -- or should we say dad's?

During an appearance on Jimmy Kimmel Live, Katherine's famous father, Arnold Schwarzenegger, weighed in on why the expectant parents might keep the sex of their next family member a secret -- at least from him. 

"I do blow it a lot of times," he said. "I can't shut my mouth."

While Arnold confirmed he currently does not know the sex of their baby on the way, he acknowledged it's possible that Katherine and Chris do and just have not shared it with him. However, if she's anything like her mom -- his ex, Maria Shriver -- then Arnold is leaning toward his daughter not knowing at all. 

"I remember that my wife never wanted to know," he recalled. "It was always a guessing kind of a game."

Continued Arnold, "I think because Katherine is a lot like Maria, I think that she probably would go in the same direction and not want to know."

"This just a guess," he clarified, "and also she cannot trust me."

Meanwhile, it sounds like the father of five has been enjoying his new role as grandpa to the couple's first child together, 1-year-old Lyla. "It is the easiest thing to be a grandfather," he told host Jimmy Kimmel. "They come over to the house, you know, you play with Lyla for around an hour or two, I put her on the horse, I put her with the dog, I play with the dog and, after two hours, they leave."

Jokes aside, the 74-year-old actor said "the whole house lights up" when they come over. 

"He’s a fantastic guy and a great son-in-law," Arnold said of Chris. "I love my daughter. Katherine is so wonderful and I'm so proud of her."