SINN Fein assembly member Phil Flanagan has been forced to apologise after sharing a sexually vulgar tweet about the Duke and Duchess of Cambridge on his Twitter page.

The Fermanagh-south Tyrone MLA 'retweeted' the crude comment to his 3,600 plus followers on Monday evening before news was announced of the birth of the Royal couple's first child.

The unsavoury tweet written by user @Threepwood2012 and shared on the social-networking site by Mr Flanagan and others read: "The news says that duchess doll entered the hospital via a back entrance. If William had done the same we wouldn't have to suffer this balls."

Mr Flanagan also 'favourited' the tweet which was just one of several tweets visible on his Twitter page that poked fun at, or was critical of, the Royal family, but by far the most offensive.

Yesterday (Wednesday) the politician and father-of-two apologised saying he retweeted the tweet "in a split second error of judgement."

In a statement to The Impartial Reporter, Mr Flanagan said: "In a split second error of judgement, I misconstrued the meaning of this tweet and re-tweeted it to my followers in that context. I innocently believed that this joke was about an expectant father being spotted entering the hospital through the front door, leading to a two day media circus with no news to report."

He added: "In hindsight, I can now understand the potential double meaning that some may read into this, but this was not my intention. I apologise for any offence that this may have caused anyone."

It is not known if by retweeting the remark Mr Flanagan breached the MLA Code of Conduct which states: "Members should keep in mind that rude and offensive behaviour may lower the public's regard for, and confidence in, Members and the Assembly itself. Members should therefore show respect and consideration for others at all times."

Last year Ulster Unionist MLA Tom Elliott said he was considering reporting Mr Flanagan to the the Standards and Privileges Committee at Stormont for referring to him as a 'clampit' on Twitter. Mr Flanagan used the word [which means hill-billy] to describe Mr Elliott and UUP leader, Mike Nesbitt.