"Actually I got on the scale today and it said that I am down 50lbs," the beaming new mum said, flaunting her figure in a sheer white lace dress, her black underwear on display. "That made me excited."
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The 33-year-old - who has lost the equivalent of 3.5 stone, or 22.6 kilos - admitted that gaining weight while pregnant with daughter North West was "the greatest challenge of my life".
And commenting on the cruel weight jibes she had to endure while expecting, she said she really took them to heart.
"It really hurt my soul," she revealed. "It changed how I am in public a little bit. I've tried to live more of a private life."
The Keeping Up With The Kardashian star lost her baby weight using the Atkins Diet, but she attributed some pregnancy swelling to preeclampsia, a life-threatening condition that raises blood pressure and which, she said, led to her five-week premature delivery.
Thankfully now Kim is back to full health – and looking forward to the future.
"I'm very happy right now," she said, as she opened up about boyfriend Kanye West's birthday proposal; "the most magical night of my life".
"I thought we were just going to dinner for my birthday," Kim explained. "He just told me to close my eyes…
"My favourite Lana song started playing, Lana Del Rey Young and Beautiful. And I was like, 'Oh my god, he got Lana to play for me on my birthday'.
"I thought that was my birthday surprise. And she doesn't get out and he goes down on his knee, and I was shaking the entire time.
"The big scoreboard said 'Please marry me'. I said 'yes'."
Kim said that she and Kanye haven't had the chance to make wedding plans yet, but said it was up to her husband-to-be.
"I want (Kanye) to have whatever he wants," she admitted, adding that "someplace Parisian" might be an option.
She also confirmed that, despite his split from her mother Kris Jenner, step-father Bruce Jenner will be walking her down the aisle.
Kim's baby daughter Nori of course got a mention, with her proud mama describing the four-month-old as "the sweetest little girl".
"She never cries. She's a perfect little angel," revealed Kim, who confirmed her plans to take Kanye's surname. "I hope she grows up to be smart and opinionated like her dad."