Simon Danczuk, the outspoken Labour MP with a colourful private life, has been suspended from the Labour Party after being accused of sending inappropriate texts to a 17-year-old girl.
Labour leader Jeremy Corbyn has confirmed the suspension.
Mr Danczuk, a Rochdale MP and leading campaigner against child sex abuse, immediately apologised.
He tweeted: "My behaviour was inappropriate & I apologise unreservedly to everyone I've let down. I was stupid & there's no fool like an old fool."
One of Mr Corbyn's fiercest critics, Mr Danczuk is facing allegations in The Sun that he bombarded Sophena Houlihan, a performing arts student, after she contacted him about a job.
Announcing his suspension, a Labour spokesman said: "The general secretary of the Labour Party has today suspended Simon Danczuk's membership of the party, pending an investigation into allegations published in the media today.
"A full investigation will now take place under the authority of the National Executive Committee, which will be responsible for determining any further action."
Mr Danczuk immediately responded by declaring on Twitter: "Today's Sun story, while not entirely accurate, refers to an extremely low point in my life."
A minute later, he tweeted an apology and then added: "I'm more saddened that this episode could overshadow the important work we're doing to help Rochdale & that's where my focus lies."
According to The Sun, the teenager, now 18, said the 49-year-old MP sent her numerous messages after he split from his wife Karen, who in recent years became almost as famous as her husband because of her own revealing selfies.
Karen Danczuk has become almost as famous as her husband
Miss Houlihan told the newspaper: "When I first got in touch I never expected the messages to get so graphic. At the time I played along with it, but now I feel like he duped me.
"I was keen for a career in politics and he is a very high profile MP and I was in awe of him."
A few months ago Mr Danczuk began a new relationship with a Labour councillor, Claire Hamilton, who he met at the Labour Party conference in Brighton. But earlier this week she claimed she had now dumped him.
The investigation by Labour's national executive is potentially serious for Mr Danczuk. The Labour leader has been tightening his grip on the party's ruling body since his shock victory in the leadership election in September.
And supporters of Mr Corbyn will shed few tears for Mr Danczuk, who has been savage in some of his criticism of the Labour leader.
On Mr Corbyn’s 100th day as leader, asked on Sky News to rate his leader's performance he said he would award him a "".
After being summoned to a meeting with Mr Corbyn in October after unleashing a barrage of criticism, Mr Danczuk wrote in the Mail on Sunday: "We need a leader who can win a General Election, not parliamentary beard of the year.
"Spending 40 minutes with him has not changed my view: he is unsuited to leading a major political party and the sooner we get a Labour leader who is, the better."
And attacking Mr Corbyn's response to the Paris attacks in November, he wrote in The Sun: "The country needs a leader with the same passion for eliminating terrorism as tackling poverty. Confronting terrorism is one of the biggest challenges of our time.
"Until he makes it one of Labour's biggest priorities, Jeremy Corbyn won't be taken seriously."