Allen also brought up Cole's 2003 conviction for attacking a nightclub toilet attendant in the message referencing Harding's "terrible fight" with Theo de Vries, for which both of the former couple could face assault charges.
In a post on Wednesday (January 4), Allen noted: "wow 40% of Girls Aloud will have been charged with assault" and refused to back down when showbiz reporter Dan Wootton described the comment as "typically bitchy".
As he accused Allen of having an "irrational hate" of Girls Aloud and reminded her of the apparent truce with Cole, the 26-year-old replied: "errrrr inaccurate ! I LOVE girls aloud 'Promise' is mine and [husband] Sam Cooper's song."
Cole later appeared to have unfollowed Allen, as she tweeted: 'I've been on here 4 months but still feel a little new to this.. What does this button do...???'"
The singers seemed to call an end to their bickering in October when Cole congratulated Allen on her pregnancy.
The ill-feeling began in 2007 when Cole labelled Allen as a "chick with a d**k" after referring to her Girls Aloud bandmate Nicola Roberts as "the ugly one".
Allen responded by calling the 28-year-old a "stupid bitch" and accusing her of lacking talent.