Karlie Kloss Engaged to Joshua Kushner

Karlie Kloss is engaged to boyfriend Joshua Kushner after six years of dating, with the model sharing the happy news on Instagram Tuesday.

The 25-year-old marked the occasion with a photo of herself giving Kushner a kiss on the cheek as the sun set over the water behind them.

"I love you more than I have words to express," she wrote. "Josh, you're my best friend and my soulmate. I can't wait for forever together. Yes a million times over."

"He proposed a few weeks ago during a romantic weekend together in upstate New York," a source told PEOPLE. "They're both overjoyed and happily celebrating. Their hearts are full and they're excited to build their future together."

The couple is currently celebrating their engagement while vacationing in Italy.

A source shared that ahead of the engagement, Kloss converted to Judaism in June.

"She's never been one to make decisions lightly," the insider said. "She spends a lot of time reflecting and learning."

Kloss and Kushner have been dating since 2012. In 2013, Kloss told PEOPLE that she enjoyed the fact that her boyfriend is "so not in fashion. It's really refreshing to leave all the fashion shows and shoots and chaos totally behind."

The couple has been notoriously private when it comes to speaking about their relationship, something Kloss shared is intentional.

"It's not like I've ever wanted to be so secretive about my private life," she told Porter magazine this year, via Harper's Bazaar. "Carolina Herrera always says, 'A woman who's an open book is boring.' There's no mystery anymore. I know in my life what really matters to me. I'm not trying to hide that from the world; I just really like having a more private private life. I've got nothing to hide, though!"

The duo has attended a handful of high-profile events, including this year's Met Gala, and will occasionally share sweet posts about each other on social media.

In April, Kloss posted a shot of the duo sitting in an ATV in the desert, writing, "My ride or die."

Kushner is the younger brother of Jared Kushner, a senior advisor to the president and husband to Ivanka Trump. Kloss previously stated that she voted for Hillary Clinton in the 2016 election while a rep for Joshua told Esquire at the time that the entrepreneur "is a lifelong Democrat and will not be voting for Donald Trump."

Photo Credit: Getty / James Devaney