Mark and Becca with their baby girl Presley, born in October (Image: Mercury Press & Media)

A mum who has just welcomed her first child is thought to be Britain's youngest grandmother at 21 after tying the knot with a granddad.

Becca Keeley married 56-year-old Mark after they got engaged on holiday in Tenerife and is now a step-gran after the birth of seven-month-old Mollie.

The couple, of Gravesend, Kent, met at a rock concert in which singer Mark was performing with his band when Becca was just 16 and he was 51.

She's six years younger than his oldest child from a previous relationship and the same age as one of the others, reports The Sun.

 Becca Keeley, 21, married 56-year-old granddad Mark two years ago after when she was just 16 (Image: Mercury Press & Media)

Last October they welcomed a child of their own, four-month-old daughter Presley, having been happily married for two years.

Mark's other kids are Aaron, 27, Jake, 21, Luke, 16, and Emma, 13.

Former office manager Becca doesn't mind being called a grandmother despite Mark initially advising her to go find someone her own age.

Becca said: “Mark said I surely wouldn’t want to be called nan but his family are my family.”

Mark said: “A lot of people thought it was wrong. I told her to find someone her own age but we made each other so happy we decided to try and conquer it.”

 The loved up pair regularly shared romantic selfies on social media (Image: Mercury Press & Media)

They married at Maidstone register office in Kent in front of 300 guests in August 2018 and regularly share loved up selfies on social media.

Rocker Mark has just released a new album called Return to Sender and still regularly performs live.

The world’s youngest grandmother by birth is believed to be Rifca Stanescu, from Romania, who became a gran at 23.

She had her first child Maria, aged 12.

Rifca said in 2016 she “wished more” for her daughter, but was happy to be a gran.

Britain’s youngest gran was an unnamed 26-year-old from Rotherham, Yorkshire, as her daughter, 12, gave birth in 1999.

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