Katherine Schwarzenegger's mum Maria Shriver has revealed her daughter is "super happy" about her engagement to actor Chris Pratt.

Shriver appeared on the Today show on Tuesday where she was asked about the happy news.

"She's super happy - and gave me very strict instructions not to talk about it," the journalist and author responded. "She said, 'It’s not your moment!'

"I'm like, 'I’m clear.' I gave her that line!"

Pratt announced their engagement earlier in January by posting a picture to Instagram of him embracing Schwarzenegger, who is sporting a large diamond ring on her left hand.

He wrote in the caption: "Sweet Katherine, so happy you said yes! I'm thrilled to be marrying you. Proud to live boldly in faith with you. Here we go!"

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Shriver added that she will keep schtum about any further details.

"No one wants to hear from me. It's not my moment. I know nothing, I say nothing," she said with a laugh.

When correspondent Jenna Bush Hager suggested Schwarzenegger will want to "keep whatever she can private", Shriver responded "That's right, exactly," she said, and then quipped: "Good luck."

Shriver previously publicly congratulated the couple on their engagement with an Instagram comment.

"Congratulations to two loving, kind, caring, thoughtful, spiritual people. We are so happy for you. You are blessed, as is everyone who knows you. Yes, let's go." 

Pratt confirmed his romance with Schwarzenegger in December when he wished her a happy birthday and posted a collage of photos of them together.

He wrote: "Happy Birthday Chief! Your smile lights up the room. I've cherished our time together. Thrilled God put you in my life. Thankful for the laughs, kisses, talks, hikes, love and care."

It was the first time either of them had addressed their relationship publicly.

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Pratt's ex-wife Anna Faris was among those offering their congratulations to the happy couple.

She wrote on Twitter: "I'm so happy for you both!! Congratulations!"

The actress later revealed she offered to officiate their wedding as she is an ordained minister.

Pratt and Faris' divorce was finalised in October last year. The couple have a six-year-old son, Jack.