(Reuters) - Bristol Palin, a daughter of 2008 Republican vice presidential candidate Sarah Palin, has given birth to a second child out of wedlock.

Palin, 25, who has been an advocate of sexual abstinence before marriage, tweeted on Thursday that she had given birth to a girl, Sailor Grace. "My Heart Just Doubled," she wrote.

The father was not named. Palin announced she was pregnant in June, a few weeks after her engagement to Medal of Honor winner Dakota Meyer was called off.

Her first pregnancy as a teenager gained widespread attention in 2008 when it was disclosed during her mother's campaign as the running mate of Republican presidential nominee Senator John McCain.

Sarah Palin, a former Alaska governor, tweeted that the baby was born late on Wednesday. "Oh, perfect love! The best gift ever!" she wrote.

(Reporting by Ian Simpson; Editing by Leslie Adler)