The Liverpudlian crooner made the swipe on Twitter, tweeting the star directly to wish her a 'nice day' with a link to the definition of the word 'karma'. Ouch.
While Christopher was competing on 'The X Factor', Tulisa regularly criticised his performances for being dated and old fashioned, and six months on it looks like someone is still bearing a grudge.
The news that Tulisa had allegedly been caught on camera setting up a drugs deal by an undercover reporter from The Sun broke on Sunday, and it has since been reported that she could face arrest.
She could also lose £1m in valuable endorsement deals. Bank clothing - with whom Tulisa has a clothing line - are considering ditching her in the wake of the controversy.