"In the hospital thanks to @khloekardashian," the 16-year-old reality star captioned a picture of herself covering half her face with her hand. "My mom said, 'Never thought I would take u to the doctor for a trampoline accident at this age.'"
Then, in a message to her sister, she wrote, "This means war, Khloe. P.S. It was painful taking this photo."
It's not clear exactly what happened between the two, but a collage on Kardashian's Instagram account shows the two falling down on the trampoline with their arms and legs intertwined. "This started out calm and ended in a war!" the 29-year-old Keeping Up With the Kardashians regular noted. "Sorry @kyliejenner."
Alongside another picture -- this one showing Jenner clutching her back as she fell separately from Kardashian -- the newly single star wrote, "Kylie, this is proof you did it to yourself! Sorry not sorry! Just kidding, I am sorry my little bug a boo. Let the war continue!!!"