Sarah Palin's 18-year-old daughter Bristol has reportedly given birth to a son. Tripp Easton Mitchell Johnston was born on Sunday and weighed 7lb 4oz (3.3 kilogram). "The baby is fine and Bristol is doing well. Everyone is excited," Sarah Palin's aunt Colleen Jones told a magazine. Shortly after being chosen as Republican presidential candidate John McCain's vice presidential running mate last summer, Sarah Palin revealed that her 18-year-old daughter was pregnant. The announcement won big headlines on the first day of the Republican National Convention in September. Mrs Palin said Bristol, who was 17 at the time, intended to marry the father, Levi Johnston a former high school classmate. Mr McCain's Democratic opponent Barack Obama, who went on to win the election, told supporters to respect the Palin family's privacy. Conservatives praised Bristol Palin's decision to have the baby rather than seeking an abortion. Mr Johnston's mother, Sherry, was arrested on drug charges earlier this month after an undercover narcotics investigation. Mrs Palin and husband Todd have five children Track, Bristol, Willow, Piper and Trig.