Dappy has been forced to apologise to the widow of murdered headmaster Philip Lawrence after paying tribute to his killer in a new music video.
Dappy's Tarzan 2 video features several names in the opening credits, including "Free Leo Chindamo", the 15-year-old who stabbed the teacher to death outside a London school in 1995.
The message caused outrage with Lawrence's family, and his widow Frances told The Sun: "I haven't heard the song yet. But I don't think it is right someone should be making money from using his name in a song."
But now Dappy, who went to school with Chindamo's brother, claims he was not aware of the thug's criminal past - and has said sorry for causing the Lawrence family further pain.
In a statement on his Twitter, he wrote: "Just wanted to say I honestly wasn't aware he did that, I knew his brother from when I was young.
"In no way did I intend to cause any upset and certainly didn't know about his past. My heart goes out to Mr Laurence's family and I know the pain of losing a loved one, sincerely Daps."
Chindamo was released in 2010 after serving 12 years behind bars, but was jailed again just four months later after being arrested over allegations of robbery. He was later cleared.
The track is set to be the rapper's most controversial song to date - he's already fallen out with former N-Dubz bandmate and cousin Tulisa Contostavlos after slamming her boss Simon Cowell and The X Factor in the lyrics.
In the song, he raps: "I heard Simon Cowell thinks I'm a little w***er/ And that I'm getting on his t**s like cancer/ I don't want to start mentioning names (f**k it)/ Where they all now? They're bankrupt. Joe McElderry, oh what a stand up/ Alexandra (Burke), pull your socks up/ Where your hits at, you ain't no winner/ I feel bad cos your voice is amazing/ But your career is getting raped by a mason."
Tulisa, who returns as a judge on the talent show this year, slammed Dappy's choice of words, insisting she did not condone the song.
She wrote on Twitter: "Just puttin it out there. dont involve me in dappy's latest hype, I don't condone it in anyway. N its a shame I'm not around 2 control him (sic)."