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Cadet has died in a car crash on the way to a gig in Staffordshire.
The rapper's family shared the news on his official Instagram account.
"We the family of Blaine Cameron Johnson otherwise known as Cadet (Underrated Legend) would like to share the sad news that during the early hours of 9th February 2019 he passed away."
In a statement to Radio 1 Newsbeat, his management said the 28-year-old was a passenger in a taxi.
He was on his way to Keele University where he was due to perform.
In a statement, Staffordshire Police said: "Emergency services attended and a passenger of the Toyota, a 28-year-old man from London, sadly died at the scene.
"The drivers of both vehicles, a 36-year-old man from Stoke-on-Trent and a 22-year-old man from Crewe, were taken to the Royal Stoke University Hospital with serious injuries.
"Three further passengers of the Toyota were treated at Leighton Hospital in Crewe."
Cadet's cousin Krept led the tributes online, saying he was "heartbroken".
DJ Semtex posted on Twitter: "I can't believe it", adding that it was going to be Cadet's year.
Cadet regularly appeared on BBC Radio 1Xtra performing at MistaJam's Christmas Party last year.
Cadet was due to perform at Wireless in July.
In a statement on the festival's website, it said: "Our thoughts and prayers go out to the family, friends and fans, of Cadet.
"Such sad news.
"We'll be keeping his Wireless performance as a time to reflect on the memory of Blaine."
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