Olajide William "JJ" Olatunji, better known by his YouTube name KSI, told Justin Bieber that he better be there to watch him fight Logan Paul. The amateur said he wants to see the singer's reaction when he takes down his opponent on the ring.

KSI did not mince his words when he told the Canadian singer to "f**k" off. He explicitly said, "F**k you, Justin."

The threat comes after Bieber made it known last month that he is #TeamLogan. The "Love Yourself" singer commented on the announcement for the pair's Nov. 9 fight at Staples Square and wrote, "rip his head off."

KSI wants the 25-year-old musician to know that he chose the wrong side. He wants to show what he is capable of doing when he knocks Paul out.

"If anything, it's gonna be more funny when I knock out Logan," KSI told TMZ Sports.

The amateur boxer just laughed at Bieber's comment. He said he "f***ing died" when he saw the singer telling Paul what to do. He admitted though, that it is cool that Bieber knows him.

"I hope Justin Bieber's gonna be ringside, so after I knock out Logan, I can be like, 'Whose head was gonna get ripped off?!? You prick,'" KSI added.

On the other hand, Paul said Bieber is smart for choosing his side. He also assured the singer that he will carry out his instructions. Paul said if Bieber wants KSI's head off, then he is going to do it.

Ahead of their Nov. 9 rematch, KSI and Paul will meet for a UK press conference in London on Oct. 7. It would be their second face-off after they exchanged weak insults during their first meeting.

The YouTube stars' boxing fight reportedly drew controversy since they have never been involved in any professional fights before. Their rematch is slated for the main event while WBO super middleweight champion Billy Joe Saunders and lightweight prospect Devin Haney will play the undercard.

Ahead of the KSI vs. Logan Paul fight, KSI wants Bieber to know that his words will serve as his motivation. Now that the superstar is involved, he vows to show the singer that he chose the wrong boxer.

KSI
KSI, whose real name is Olajide "JJ" Olatunji,launched his YouTube channel in 2009.
Justin Bieber