The Nottingham Panthers star, 29, died in hospital after suffering a gash to the neck in a collision with a Matt Petgrave on Saturday.
Johnson’s girlfriend Ryan Wolfe was among 8,000 people watching the game against Sheffield Steelers at the Utilita Arena when the tragedy unfolded.
She rushed down to the ice to be by his side as the players formed a ring around him, before protective screens were brought onto the rink.
The couple had been living together in England, with Johnson studying at Loughborough Business School alongside ice hockey.
His aunt Kari has revealed how the US-born forward was planning to propose to Ryan.
She said: “We were all really excited because we were really looking forward to their future and he didn’t get a chance to ask her, and then this happened.”
Johnson immediately fell to the floor after he was struck in the neck by the ice skate of Matt Petgrave 35 minutes into the game.
He was helped towards the side of the rink by a teammate, but collapsed a few paces later.
Johnson received emergency treatment at the scene, before being rushed Sheffield’s Northern General Hospital, but later died as a result of his injuries.
Kari was watching the game on a live-stream from her home in Minnesota when the “horrific” collision took place.
She told local outlet KSTP-TV: “We saw it happen. It was horrific. I cannot even describe it because nobody should have to live through what we saw.
“The skate cut right through Adam’s windpipe, and it cut his carotid artery. At one point, they had lost him in the ambulance and they brought him back.
“He didn’t make it through surgery once they got him to the hospital.
“They just couldn’t get the bleeding to stop. He lost way too much blood. Just seeing it was traumatic.”
An inquest was opened into Johnson’ tragic death today.
The brief hearing was told how his Ryan identified her boyfriend’s body after he died in hospital later that day.
No cause of death was revealed during the brief hearing in Sheffield but Sheffield Coroner Tanyka Rawden said Johnson was “seriously injured”.
The full inquest was adjourned until January 26, 2024, while an investigation into his death continues.
Ms Rawden concluded: “I would like to take this opportunity to offer to Mr Johnson’s family, friends and everyone that knew him my sincere condolences.”
South Yorkshire Police is investigating the death, but has warned its probe will take “some time”.