TO THE millions of fans who know her as Lady Grantham the chatelaine of Downton Abbey, she is the slightly feisty but still nevertheless quite reserved epitome of an upper-crust lady.

How many fans, however, who enjoy the trials and tribulations of the Granthams as they struggle with life upstairs and downstairs at the Abbey, realise that Cora, Countess of Grantham is really a rocker at heart.

In fact, Her Ladyship is quite relaxed letting her hair down and belting out a mean tune in real life as American-born singer and actress Elizabeth McGovern.

Now she is to appear with her band Sadie and The Hotheads at the Isle of Wight Festival. She will also take to the main stage to sing with Scottish rockers Big Country, one of the top acts from last year’s festival.

Elizabeth, who has appeared on screen in such films as Once Upon a Time in America, Ragtime, and Ordinary People will take to the stage during the festival on June 23.

Elizabeth helps writes her band’s songs and is said to have entertained fellow Downton cast members down the pub by performing jazz. She has also been reported to be joining forces with co-star Michelle Dockery, who plays her daughter Lady Mary in the drama, to record an album together.

Isle of Wight Festival promoter John Giddings said: “I have been a fan since Once Upon A Time In America. As soon as I found out that Elizabeth could sing, it was a must to invite her to play at the festival. We will roll out the red carpet for Lady Cora.”

Headliners for the festival, which runs for three days from June 22, include Tom Petty and the Heart-breakers, Pearl Jam and Bruce Spring-steen.

Elizabeth said she was thrilled to be playing with such a “stellar cast of musicians”.

Elizabeth moved to live in London 20 years ago and is married to Simon Curtis who directed the recent smash hit movie My Week with Marilyn.