Two women who only discovered they were sisters three years ago have now been told they are twins.

The news has come as a shock to both Jenny Lucas and Helen Edwards – not least Helen, who is 15 months older than she thought she was.

"This has been a real rollercoaster of emotions," she said. "I have been lied to about my birth all my life.

"All the big dates in my life, like my 21st birthday, have been false."

Jenny and Helen celebrated their first birthday together at a surprise party on Saturday.

Both women were 64 on Sunday, although until earlier this year, Helen thought she was only 62.

The story of how former professional golfer Jenny, of Smallhythe Road, Tenterden, and Helen, who lives in Northumberland, discovered they were sisters was revealed earlier this year.

Jenny had been given up for adoption when she was born and two women grew up in different circumstances, neither knowing of the other's existance, until Jenny met their mother in 2003.

They thought they were half-sisters until DNA tests in 2009 revealed a 99% certainty that they were full sisters.

The twins revelation came about a few months ago when Helen discovered her birth had been registered on two occasions.

She applied for their late mother's medical records which showed no birth on April 4, 1950 – the day she thought she was born – but there was a birth on December 2, 1948, which is Jenny's birthday.

"I spoke to a couple of DNA labs and they said there was a twins test we could do," said Jenny.

"all the big dates in my life, like my 21st birthday, have been false" – helen edwards

"Parts of our DNA were tested and came back with the result that we were twins. Our mother's medical records showed she had had five children, but all had been home births apart from the one in December, 1948, when she had been in hospital for 11 days which must have been because she had twins."

Helen said they were both coming to terms with the news.

"This has been an incredible shock and it has been a very difficult time," she said.

"Jenny and I have gone through a real rollercoaster with this whole story. Discovering we were twins was happy news but a real shock.

"For twins to be separated at birth is hugely emotional, but does go some way to explain the similarities between us – we were brought up differently but are so alike."

The birthday party at The Tenterden Club on Saturday was a surprise for Helen, who just thought they were going for a family meal.

Around 60 people attended and the two women cut a cake together.

They have written a book about their reunion, called My Secret Sister, which is published on March 14, next year, but can be ordered now.

It is by Helen and Jenny, writing under her maiden and professional golf name of Jenny Lee Smith.