Sarah Palin in 'fake baby' storm

Presidential hopeful John McCain's running-mate found herself at the centre of a growing storm today as she was forced to deny internet rumours that her fifth child is really her GRAND-DAUGHTER.

Only hours after spoof nude photos of Sarah Palin sent the web into a frenzy, the former beauty queen was accused of faking pregnancy to cover up for her unmarried daughter Bristol, 17. Trigg was born in May with Downs Syndrome.

Today, the conspiracy took a new twist. Anti-McCain bloggers claimed the shock news that Bristol, 17, is now five-months pregnant was announced to divert attention from the alleged cover-up.

The deluge of rumour has been DENIED by McCain's camp but could tarnish Republican Sarah's reputation as a typical 'hockey mom' among America's influential Christian right.

Sarah confirmed last night that Bristol was pregnant and would marry her boyfriend Levi. She said she had made the statement to counter "mud-slinging and lies" about the cover-up conspiracy.

In a joint statement, Mrs Palin and her husband Todd said: "We're proud of Bristol's decision to have her baby and even prouder to become grandparents. Bristol and the young man she will marry are going to realise very quickly the difficulties of raising a child, which is why they will have the love and support of our entire family."

Sources in McCain's camp said: "Senator McCain's view is this is a private family matter. Life happens."

There was no indication that the rumours would put Sarah's position in jeopardy, but the questions swirling around her on the first day of the Republican National Convention, already disrupted by Hurricane Gustav, have caused some Republicans to worry that Democrats would use the selection to question McCain’s judgment.

And questions are also being raised about whether the 44-year-old former Alaska Governor has enough experience to stand in as America's commander-in-chief should anything happen to 72-year-old Mr McCain.

Barack Obama, McCain's opponent to become the next US President, has denied anyone in his camp is responsible for spreading the rumours about Sarah and said he would fire anyone caught doing so.