Levi Johnston and Bristol Palin had been dating for three years
Bristol Palin, the 18-year-old daughter of Alaska Governor Sarah Palin, has split from her fiance, Levi Johnston.
Miss Palin's pregnancy by Mr Johnston, 19, made headlines shortly after Sarah Palin was named as John McCain's running mate in last year's elections.
The couple's son, Tripp Johnston, was born in December.
Mr Johnston told Associated Press (AP) that the couple had mutually decided "a while ago" to end their three-year relationship.
Speaking outside his family's home in Wasilla, north of Anchorage, Mr Johnston said some speculation about the break-up, circulating on the internet, had been inaccurate.
In a statement issued through Sarah Palin's political action committee, Miss Palin said she had been "devastated" by some media intrusion into their relationship.
"Unfortunately, my family has seen many people say and do many things to 'cash in' on the Palin name," said the statement.
"Sometimes that greed clouds good judgment and the truth."
Sarah Palin's spokesman, Bill McAllister, declined to comment on the break-up.
The Alaska governor revealed her daughter's pregnancy - and engagement - just days after being named as the Republican vice-presidential candidate by John McCain.
Mrs Palin is a social conservative who is opposed to abortion and the pregnancy became a talking point during the campaign.
In December, Mrs Palin said that her daughter and Mr Johnston were "committed to accomplish what millions of other young parents have accomplished, to provide a loving and secure environment for their child."
Bristol Palin said in an interview with Fox News last month that Mr Johnston saw the baby every day and described him as a "hands-on" father.
The couple had said they were considering a summer wedding.