The "Keeping Up with the Kardashians" beauty reveals their five-year-old daughter North came up with the master plan, and recruited brother Saint, three, to help trick their rapper dad.
Kim admits she was rather pleased to see the siblings bonding as North had initially struggled to accept that she wasn't the baby of the family anymore once Saint arrived.
"(They are) starting to get closer now that (North) can include him in her jokes," she told Elle.com on Tuesday, April 02.
"She roped him into an April Fools' prank yesterday that was ridiculous. She took ketchup into my bathroom, and she begged me to let her spread it on me, and on the bathroom, as if it was like a bad scary movie. Then she asked me to lie down."
Kim continued, "I thought she was just playing, maybe that she was going to say I was hurt. No. She taught Saint how to fake cry - she showed him how to do it! - and then she told him to scream, 'Mommy's dead!'."
However, the prank fell flat with Kanye, who rushed to check on his wife.
"Kanye ran upstairs and he was like, 'Kids, this is not funny. This is not a good prank'," she shared. "I completely understand and I agree."
But the 38-year-old was still quietly cheering North and Saint on: "It did make me a little impressed that they planned something together, and they were getting along and having fun as a team."
Kanye had good reason not to be amused by the death prank after Kim's horrifying robbery ordeal in Paris, France in October, 2016, when she was bound, gagged, and held at gunpoint as armed men ransacked her apartment suite and stole millions of dollars' worth of jewellery and electronics.
The couple, which has since bounced back from the massive security scare, also shares 14-month-old daughter Chicago, while the stars are currently expecting their fourth child, another boy, via a surrogate.