Mr Nembhard, also known by his rap name TKorStretch, was confirmed as the victim by his manager, Chris Patrick, on Tuesday morning.
The 21-year-old, from Bristol, was visiting the carnival with his sister and friends, Mr Patrick said, when the attack happened on Monday.
The rapper has more than 300,000 plays on one of his songs on Spotify and nearly 11,000 monthly listeners.
Mr Patrick said on Instagram: “Two years ago a young 19-year-old man came from Bristol to meet me at my Studio with his dad, his name was Takayo Nembhard AKA TKorStretch.
“That meeting took us on a journey…we recorded some great music together. His talent was endless and I can tell you guys he was close to greatness!
“So it’s with a heavy heart that I bring the news that Takayo (TKorStretch) passed away last night.
“He came from Bristol to simply have a good time at the London carnival and this is the end result!
“My deepest condolences to TK’s Mother & Father his Brother, 2 Sisters, Girlfriend and child that will never meet his father!
“TK was a good kid, a good guy and what has happened breaks my heart…rest in peace my friend.”
In a statement, Mr Patrick added: “As you can imagine, we are all in shock.
“He went to carnival with his younger sister and friends to have a good time. This is the worst possible ending for a talented kid.”
A family member at Mr Nembhard’s home in Bristol confirmed he died at the carnival on Monday evening, and requested they be given privacy to grieve for him.
Mr Nembhard had also been a talented schoolboy footballer, spending time as an academy player for Bristol Rovers.
In a statement, the club said: “Bristol Rovers are deeply saddened to learn of the death of former academy player Takayo Nembhard.
“The club would like to pass on its condolences to Takayo’s family and friends at this difficult time.”
The Metropolitan Police has launched a murder investigation following Mr Nembhard’s death.
The force said officers were called to reports of a stabbing under the Westway flyover in Ladbroke Grove at about 8pm on Monday.
Police and paramedics provided first aid treatment to Mr Nembhard and he was taken to hospital, where he later died.
Mayor of London Sadiq Khan said he was “sickened” by the stabbing.
“Violence has no place on our streets and we are doing everything in our power to root it out,” he said.
Police said 209 arrests had been made at the carnival by early Tuesday, including 46 for assault, 36 for possession of drugs, 33 for possession of an offensive weapon, 27 public order offences and eight sexual assaults.
There were 35 arrests the force labelled “other”, ten for possession of psychoactive substances, seven for drink/drug driving, five for criminal damage and one each for theft and robbery.