On Friday, the former NBA star woke from a coma for the first time since being found unresponsive in a Nevada brothel on Tuesday (12 October).
And, after visiting him in hospital, pregnant Kim reports that Lamar has been able to smile at his former sister-in-law from his bed.
Sharing a picture of herself with sister Khloe's ex-husband Lamar in happier times, Kim wrote: "I have faith in you. I believe in the power of prayer and positive energy! Thank you all for your prayers! Lammy- I'm so happy Kendall & I could make you smile today! God is good!"
Since Lamar's condition came to light, the Kardashian family have been asking fans to pray for the famous basketball star.
I believe in the power of prayer! Thx 4 ur prayers Lammy- So happy Kendall & I could make u smile 2day God is good! pic.twitter.com/T50WNEnmOL— Kim Kardashian West (@KimKardashian) October 18, 2015
Kris Jenner, meanwhile, posted a moving tribute to Lamar.
She tweeted: "Come on Lamar!!!! You are such a champion... I know you got this.... #ourfighter #pleasepray #love #thatsmileiseverything."
Just hours before the tweets, Kim, Kris and Kendall boarded a private jet from the Van Nuys, California, to be by Khloe's side in the Las Vegas hospital where he is recuperating.
Khloe has been by Lamar's side 24/7 since he arrived at the hospital in a coma.
A source tells Us Magazine that Khloe has become a 'shell of herself' since Lamar's collapse and that making decisions for him has 'been very hard on her'.
Although Khloe and Lamar signed divorce papers this year, they have not been finalised by a judge, so Khloe still has to make medical decisions on behalf of Lamar.
He is now said to be completely off his ventilator and is now breathing on his own.
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