An adopted woman whose birth mother has Alzheimer's broke down in tears when reading a letter from her long lost sister in this heartwarming clip.Abigail, from Yorkshire, is the mother to four children, including a little boy called Alfie who was born prematurely and died shortly after birth. Despite having a brilliant adoption, she has often thought of her birth mother ever since she was a teenager.Her birth mother, Linda, became pregnant with Abigail, who she named Rachael, at just 15 years old. She initially tried to hide the pregnancy by wearing 'really baggy clothes'.But she was soon forced to tell her traditional parents, who didn't believe in having a child out of wedlock. A heartbroken Linda was taken to a mother and baby home near Huddersfield to have her child, before Rachael was given up for adoption.Eight years ago, at the age of just 57, Linda was diagnosed with early onset Alzheimer's disease. She is now nonverbal and uses a wheelchair.Her second eldest child Melissa, 36, contacted Long Lost Family as she was desperate to find her sister: 'It's my last ditch attempt in the time that my mum's still got. I know how much it means to my mum. 'If she was able to meet Rachael. If it's something that can give her some kind of comfort in some way, that would be really positive for all of us.'The family appear on Thursday's episode, which will air at 9pm on ITV, and sees a tearful Abigail read a letter from her long lost sister, in which she's told: 'I wanted you to hear from me how loved you've always been.' Abigail (pictured), from Yorkshire, is the mother to four children, including a little boy called Alfie who was born prematurely and died shortly after birth. Despite having a brilliant adoption, she has often thought of her birth mother ever since she was a teenagerMelissa, from Tadcaster, where she lives with her husband Paul and two young children Ruby and Alfie, has always known she had an older sister who was adopted, and wants to find her before it's too late to reunite with their mother. The mother-of-two had a wonderful childhood growing up with parents Rob, Linda and younger brother George. She still lives close to them. When Melissa was about 10 years old, her mother Linda revealed that when she was aged 15 she became pregnant and had a baby. Linda told Melissa that initially she tried to hide her pregnancy, with the mother-of-two recalling: 'So she just started to wear really baggy clothes and then eventually she realised she had to tell her mum and dad. 'They didn't have a lot of money. They were quite a traditional family, if you're not married and you have a child out of wedlock, there's a stigma, this can't happen to our family.'Linda was heartbroken that she had to place her daughter up for adoption - and once she had told her younger children about Rachael's existence, she was never kept as a secret from then on.The Long Lost Family's team took on Melissa's search and discovered that Rachael is now called Abigail (Abbie for short) and lives in the same county as her sister. Abbie's birth mother, Linda, became pregnant with Abigail, who she named Rachael, at just 15 years old. She initially tried to hide the pregnancy by wearing 'really baggy clothes'. Pictured, presenter Nicky Campbell next to Abbie When Abbie (pictured) meets Nicky she shares that she has had a brilliant adoption but that her birth mother has been on her mind since she was a teenager. She is bowled over to see a photograph of Linda and delighted that Melissa has come looking for herWhen she's contacted by the programme, Abbie responds immediately that she would like to meet her birth mother. Ahead of meeting presenter Nicky Campbell, she is informed of her birth mother's dementia diagnosis.When Abbie meets Nicky she shares that she has had a brilliant adoption but that her birth mother has been on her mind since she was a teenager. She is bowled over to see a photograph of Linda and delighted that Melissa has come looking for her.Abbie tells Nicky about her family and she cannot believe that Melissa has chosen the same names for her children and is desperate to meet her sister, saying: 'It's going to be the start of something amazing, I hope'.The presenter offers Abbie a note, explaining: 'I have a letter that Melissa has written, would you share it with me?'The mother-of-four replies: 'Now I am shaking...' before asking: 'Was I called Rachael?' when she sees the start of the message.'Dear Rachael, I have known about you since I was around ten years old,' reads Melissa's letter. 'We've often wondered how your life has been and hoped that one day we might be able to find you.'I wanted you to hear from me how loved you've always been. With love, Melissa.' An emotional Abbie says: 'That's wonderful.'Long Lost Family continues on Thursday 10th September at 9pm on ITV and ITVX.