Katherine Schwarzenegger and Chris Pratt expecting third baby

Katherine Schwarzenegger and husband Chris Pratt are expecting their third baby.

The author is pregnant again, a source has confirmed to People.

Katherine, 33, and Chris, 44, already share daughter Lyla Maria, two, and Eloise Christina, 13 months. Chris is also dad to Jack, 10, with ex-wife Anna Faris.

After the news was confirmed, Katherine posted a photo on Instagram of her helping her daughters ride a horse. "Things that make me happy," she captioned the photo. "A gloomy morning followed by a barn visit." She wasn't showing her stomach, instead keeping her back to the camera.

Katherine has previously spoken about how important it is for mums of young children to ask for help when they need it.

"I'm a big believer - I feel like on Instagram we see all these mums that are like, 'I'm doing it all, I'm doing it all, I'm doing it all on my own,' blah-blah and I'm like, 'I don't want to do it all on my own,' she said at the Best Foot Forward panel lunch event in honour of Women's History Month last year.

"I want to lean on my sister, I want to lean on my mum, I want to lean on my girlfriends, my mum friends. I want to be honest and transparent and also say, 'I can't make this today. My kid's sick. She was up all night teething. I need to be a mum right now.'"

She added, "So I think being able to be open about the fact that you don't have to do it all...I think especially if you're balancing multiple roles, is saying, 'I need help today,' and that's okay."