The wrestling world has been in shock today as they learn about the untimely passing of British wrestling star Adrian McCallum, aka Lionheart.

McCallum passed away yesterday at the age of 36 and was the reigning ICW Champion. As of writing, the cause of his death is unknown.

Although he never signed with WWE, he worked matches for the company when they were in the UK doing shows. He did the same with TNA and he also competed for the ROH World Championship in 2008.

ICW issued the following statement on their Twitter account about McCallum's passing:

"We are heartbroken to learn of the tragic death of ICW World Heavyweight Champion, Adrian 'Lionheart' McCallum. Adrian was a mainstay of ICW and British professional wrestling. Most importantly, he was our friend. His passing leaves a huge hole in the lives of those who knew him."

His final tweet before his passing is truly devasting and heartbreaking.

Lionheart said in his tweet: "One day you will eat your last meal, You will smell your last flower, you will hug your friend for the last time. You might not know it's the last time, that's why you must do everything you love with passion" #Afterlife @rickygervais

Many former and present WWE superstars who had met or wrestled with McCallum on the UK indie scene or on the world independent circuit mourned his death.

Pete Dunne said: I always looked up to Lionheart’s professional approach to wrestling when it was far from that at the time. People like him were pivotal in the growth of a scene that has lead to so many people being able to do this for a living.

"Thoughts are with those close to him."

Paige said: "Breaks my heart. RIP my friend. You were always so wonderful to me and I’ll be forever grateful that I knew you. Give Trav a big hug from me. ❤️"

Stu Bennett, aka Wade Barrett, said: "That is awful. Met Lionheart a few times over the years and worked with him last summer at WOS. A nice guy and a talented performer. RIP Adrian."

Drew McIntyre said: "Sleep well my brother. I’ll see you down the line #RIPLionheart"

Nikki Cross said: "I’m so sorry to Adrian’s friends and family, I don’t know what to say. everyone, please think of them during this time. Rest easy Pal, your brothers and sisters will see you in another dream."

RIP Lionheart, you will be missed.