Ms Gwen, 24, from Chorley will be competing in the beauty contest this year after already winning Miss Preston GB. Niamh’s mother, Donna, 59, used a genealogy website which made the shocking revelation of the royal connection.
The research showed that the beauty queen and her mother are related to Diana’s 13th great grandmother and her 15th great grandfather.
The Miss Great Britain finalist said: “My mum was interested in finding out her ancestry and wanted to log it while she still knew a few generations prior.
“We are related to both Princess Diana’s 13th great grandma and 15th great grandad too (so not castle worthy but still exciting!).”
She added: “Me and my brother, Dean, thought she was joking.
“We absolutely adore Diana, who doesn’t?”
Both Niamh and her brother used the new information to their advantage after making the discovery.
She said: “Both of us of course milked it with friends and family (‘it all makes sense, I knew I was royal etc’).
“My brother chuckled because he actually has a keyring of Lady Diana on his house keys!”
Like all royals, distant or otherwise, Niamh supports many charitable causes as an ambassador for Mind, an advice and support service for those struggling with their mental health.
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“I’d never been a big sunbather and I have dark colouring, so I never thought I’d need to worry but when I went to the hospital for it to be checked they wanted it removed then and there.”
She added: “It was very scary but luckily it wasn’t melanoma, but I’m still very wary about sunbathing, sun beds and I always wear factor 50 in the sun.”
The month of May is Skin Cancer Awareness month, for which Niamh is collaborating with Cancer Research to teach more people the importance of checking yourself and seeing a doctor.