Sarah Palin has become a grandmother after her 18-year-old unmarried daughter gave birth to a son – Tripp Easton Mitchell Johnston.

The 7lb 4oz boy was born to Bristol Palin in Alaska on Saturday. His birth was reported by People, the celebrity magazine, which reportedly paid up to $300,000 (£208,000) for the first photographs of the baby after a bidding war among several supermarket weeklies.

Mrs Palin, 44, the Governor of Alaska and John McCain’s former vice-presidential running-mate, was forced to announce that her teenage daughter was pregnant on September 1, just after she was picked and on the first day of the Republican National Convention.

Bristol’s pregnancy has certainly been eventful. The father is Levi Johnston, a Wasilla High School ice-hockey star who dropped out early to take a job in Alaska’s North Slope oilfields as an apprentice electrician. The two are engaged and are considering a summer wedding.

After the pregnancy was revealed, Mr Johnston, 18, flew to Minnesota to attend the Republican convention, in the full glare of the world’s media, a turn of events he had probably not expected as he dated Bristol in quiet obscurity in the preceding months.

Mr Johnston’s mother, Sherry Johnston, was arrested on felony drug charges this month after Alaska state troopers obtained a warrant to search her home. According to court documents, she was arrested after sending text messages to two police informants in which she discussed buying the powerful prescription painkiller OxyContin.

Officials say that shortly into Mrs Palin’s campaign as Republican vice-presidential nominee, investigators intercepted a package containing 179 OxyContin pills. That led to the arrest of two suspects, who became police informants. They ultimately allegedly sold pills to Mrs Johnston wearing hidden cameras and microphones. She has been released on bail.

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