Chris Pratt and Katherine Schwarzenegger 'Can't Wait' to Give His Son Jack a Sibling: Source

Chris Pratt and Katherine Schwarzenegger are expecting their first child together this fall, multiple sources previously confirmed to PEOPLE

Chris Pratt and Katherine Schwarzenegger Pratt are thrilled to be expecting their first child together this fall — and making the news extra sweet for the couple is that the actor's 7-year-old son Jack will now be a big brother.

"After they got married, they couldn't wait to grow their family," says a source. "Jack will be a great big brother. Katherine always says that he is the sweetest, most caring boy." Adds a friend: "They can't wait for Jack to have a sibling."

Since the start of their romance, Pratt's son (with ex-wife Anna Faris) has been an integral part of the couple's relationship, often joining them on ice cream, movie and dinner dates.

"Katherine thinks Chris is an amazing dad. She allowed herself to fall in love with Chris quickly because she early on realized that he is a great family guy," says the source. "She loves being an extra mom to Jack."

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<a href="" data-inlink="true">Chris Pratt</a> and <a href="" data-inlink="true">Katherine Schwarzenegger</a>

Earlier this year, the Jurassic World: Dominion star, 40, opened up about the impact the Gift of Forgiveness author, 30, has had on him and his son.

"She has changed my life for the better in so many ways," Pratt told his pal Jason Kennedy during an appearance on E!'s In the Room. "My heart, my soul, my son I feel are all so safe with her. She's a great stepmom."

"She's, God willing, going to be a great mom one day," he continued. "She's got great parents, great siblings, she fills in all my many deficits."

After about a year of dating, the couple tied the knot last June during an intimate ceremony in Montecito, California.

"I do still feel like a newlywed. I don't know how long that's supposed to last, but I do definitely feel like a newlywed in the sense that I feel beyond lucky and blessed every single day to be married to the man that I'm married to," Schwarzenegger Pratt told PEOPLE in March. "I'm still really excited and crazy in love."

For all the details on Chris Pratt and Katherine Schwarzenegger Pratt's happy baby news, pick up the latest issue of PEOPLE, on newsstands Friday.

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