Model Karlie Kloss flashed her enormous diamond ring on Instagram just hours after she and her boyfriend of six years Joshua Kushner announced their engagement.

The former Victoria's Secret Angel shared the happy news on Instagram, describing the 33-year-old financier as her 'best friend and soulmate'.

'I love you more than I have words to express,' the 25-year-old wrote.

'Josh, you’re my best friend and my soulmate. I can’t wait for forever together.' She continued.

Shortly after their announcement, the happy couple was congratulated by Joshua's sister-in-law, first daughter Ivanka Trump, who shared a heartfelt message on Karlie's Instagram post.

'So, so happy for you and Josh! I feel blessed to have you as a sister (!!!) Karlie and look forward to the decades of happy memories we will create together as a family! [sic]' Ivanka wrote.

Joshua, meanwhile, posted a stunning picture of his girlfriend and captioned the striking snap with one word: 'Fiancé'.

Karlie and Jared, whose relationship was not made public until November 2012, five months after they began dating, and they are known for keeping their relationship incredibly private.

Having started dating in June 2012, Karlie and Joshua have only attended a handful of public events together in the six years since, and even then Joshua has avoided making an appearance on the red carpet.

The couple has also avoided making public appearances with Joshua's high-profile brother and sister-in-law.

In an April interview, Karlie opened up about her choice to remain so secretive about her relationship, explaining, 'It’s not like I’ve ever wanted to be so secretive about my private life.

'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.'

She then added: 'I’ve got nothing to hide, though!'