The singer made a trip to see six-year-old Tyla Atkin, as she battled for life after a car crash. She sang the youngster's favorite song, Rainbow.
Just hours after the visit at London's Great Ormond Street Hospital, Atkin woke up - and the girl's mother Michelle Hart is convinced the pop star's visit is to thank for her daughter's recovery.
She tells a British newspaper, "Doctors say you have to keep talking to people in comas to keep them focused and connected."
"I believe Jessie J saved Tyla. She gave my daughter back to me. I'm so grateful."