The basketball player got down on bended knee in her bedroom last Wednesday with a huge diamond ring thought to be worth $2 million after a whirlwind six-month romance.
Kim flashed the sparkling ring as she went through security today at LAX airport.
The happy couple confirmed the news in an exclusive magazine deal, giving away all the details of the proposal.
The 30-year-old tells America’s People magazine: ‘I didn’t expect this at all. I was in such shock. I never thought it would happen at home, and I never thought now.’
The New Jersey Nets player, 26, asked for her hand in marriage with a custom-made 20.5 carat Lorraine Schwartz diamond sparkler.
The 6ft 9in basketball star picked out the ring with the help of Kim’s manager mother Kris Jenner.
He enthused: ‘I just knew I wanted it to be big.’
The athlete proposed by writing ‘will you marry me’ in rose petals on her bed in her $4.8 million Beverly Hills home.
After Kim accepted, the couple celebrated with the Kardashian-Jenner clan during a family dinner.
Kim told the magazine: ‘Kris really didn’t want a big celebration, but he had jokingly told my mom he’d be fine if there were mini-horses there.
‘Later that night at the party, my mom brought out two mini-horses, covered in glitter, for us! It was hysterical!’
After People magazine announced the news, Jenner Tweeted: ‘Yippppeeee! So happy.’
She then asked Kim and Kris to give her more time to prepare for the wedding than her other daughter Khloe.
She joked: ‘PALEEEEEZE GIVE ME MORE THAN 9 DAYS!!!!!!!!!! I AM BEGGING…..’
Kim’s sister Khloe also added: ‘I can’t believe I was able to keep this a secret but now I can scream all I want about it! Kim is engaged!!!!!!!!!!!!!!!!!!!! OMG!!!!!!!!!!’
Her older sister Kourtney wrote: ‘My sister is engaged!!! I’m squealing with excitement! The princess has found her prince. I am so happy because @KimKardashian is happy!’
The couple started dating last December soon after Kim ended her brief dalliance with Canadian model Gabriel Aubry – Halle Berry’s ex.
It won’t be the first marriage for Kim, she eloped to Las Vegas with music producer Damon Thomas – 10 years her senior – when she was just 19, but divorced in 2004 after four years together.
In divorce papers, Kim alleged Thomas repeatedly beat her during their tumultuous marriage.
The producer has vehemently denied the claims and accused his ex-wife of being ‘obsessed with fame’ in an interview with In Touch magazine earlier this month.
In 2007, she famously dated rapper Ray J – who featured alongside her in a notorious sex tape.
Later that year, she started dating American football player Reggie Bush, with the pair going out on and off for two and a half years before splitting for good in March 2010.
Last year, she briefly dated Dallas Cowboys player Miles Austin for about two months.
Fans of Keeping Up With The Kardashians have long seen the socialite speak of her wish to settle down and start a family.