Kim Kardashian on Sexy Selfie: a 'Middle Finger' to Those Who Called Me Fat ...

Kim Kardashian opened up on a number of topics - from weight gain to her impending nuptials to Kanye West - during an appearance on NBC's The Tonight Show Wednesday.

She said she was hurt by paparazzi reports during her pregnancy focusing on her weight gain, saying said she had the pregnancy-related medical condition preeclampsia, which caused her to swell up.

'It was the greatest challenge of my life to have gained 50 pounds,' she told Jay Leno, adding that she's lost the weight. 'I got on the scale today, and it said I am 50 pounds down.'

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'It really did change me a lot,' Kardashian said. 'It hurt my soul. It changed how I am in the public a little bit. I would go out and there would just be photos of me anytime I was hungry...and these stories that I was like 200 pounds.'

Kardashian dismissed tabloid stories that she was 'in hiding' after her pregnancy.

'I just wanted to adjust my life a little bit. Why would I subject myself to so much negativity, especially now that I have a daughter. I just don't need that energy.

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Leno asked Kardashian about a racy self-photograph she posted online earlier this month, and she said she originally just sent it to West.

'I was like, 'babe, can I post this up?' This is my big middle finger to the world on everyone that called me fat,' she said with a laugh.

Kardashian also spoke of her recent engagement, telling Leno the ring West presented her last week is 'the best ever.'

'He's so passionate about everything in life,' she said. 'He took so much time and thought in this to make sure it was perfect.'

She said West was going to handle most of the wedding planning details, though she said she would be involved: 'He definitely knows what he wants, and I want him to have whatever he wants.'

Kardashian said they are hoping for next summer, but they are waiting until West finishes his current tour before setting the details.

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'I think somewhere destinational,' she teased. 'Maybe I'll pick the place and he'll plan it.'

Leno asked if Kardashian's stepfather Bruce Jenner - who recently separated from Kardashian's mother, Kris Jenner - would walk her down the aisle.

'Of course,' Kardashian said. 'He is my stepdad.'

And will she change her name to Kim West? The reality star said she would probably adopt her fiancé's last name and keep Kardashian as her middle name.

'My daughter has the last name West and we're a family. I want it to definitely be West.'

Kardashian's Tonight Show appearance comes weeks after West gave a long-form and surprisingly sincere interview to ABC's Jimmy Kimmel.

Watch clips of her interview below.