A downpour won’t put a damper onKatherine Schwarzenegger‘s mood!

The 29-year-old was spotted grabbing lunch with her sister, Christina, 27, on Monday, just hours after her new fiancéChris Prattrevealedthe two were engaged.

Schwarzenegger bundled up in a black raincoat and newsboy cap in the pouring rain in Los Angeles as she held a coffee in her right hand and showed off her diamond engagement ring on her left.

A restaurant source tells PEOPLE, “She was beaming and showing off her engagement ring. She has never looked happier.”

This is the first time the book author has stepped out since news of her engagement to theAvengers: Infinity Waractor, 39, broke.

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For the ring, Pratt selected a romantic oval center stone, which appears to be set on a very thin simple band for his bride-to-be.

According to jewelry expertJason Arasheben of Jason Beverly Hills, Schwarzenegger’s ring appears to be a 5-carat diamond, which he says can range anywhere in price from $150,000 to $550,000.

“That is the hottest shape right now,” Arasheben tells PEOPLE. “It seems like 10 years ago no one asked for it and now everyone does.”

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chris pratt and katherine schwarzeneggerCredit: RoundPondEstate/Instagram

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Patrick, 25, wrote, “Love you brother.”

Anna Faris, Pratt’s ex-wife, also congratulated the two, writing, “I’m so happy for you both!! Congratulations!”

“He asked for Maria and Arnold ’s blessing and was very traditional about things,” the source said.

The source added the question came as no surprise to her parents — Pratt has long been vocal about his desire to start a future with Schwarzenegger.

“Chris has been very straightforward about his intentions from the beginning,” the source said. “Over the last few months, he’s been bonding with all of Katherine’s siblings and it was clear to her entire family they would get married.”

Adds the first source, “Katherine has been very secure with Chris since they began dating. When people asked her or her family if she and Chris had a future together, it was always a ‘Yes, of course!'”

source: people.com