The final chapter has closed on a mystery surrounding a message in a bottle to a lost son.

And for Swale sculptor Sioux Peto, it has brought an emotional end to a heart-breaking story that has touched her life for seven years. She spoke to Fiona Cooper

The story began in spring 2002 when, while out walking her dogs on the beach at Warden Bay with her then 13-year-old son Kim, Sioux discovered a bright blue tear-shaped bottle washed up on the shoreline.

Inside the Evian glass water bottle was a letter tied with a pale blue ribbon.

Returning to her Sittingbourne home, Sioux discovered the letter had been written in French and contained two locks of hair - one light brown, one dark brown.

Unable to read it, Sioux sent the letter to friend - and fluent French speaker - Karen Liebreich.

A few months later, Karen sent the translation to Sioux, who was totally unprepared for the impact it would have on her.

The letter, which has been written by a mother grieving for her lost 13-year-old son Maurice, left Sioux in tears, devastated.

"That's the only time I have ever been able to read it," said Sioux. "Even now it gives me goose bumps thinking about it; it's like your worst nightmare."

Unable to banish the letter's contents from her mind, Sioux's friend Karen embarked on a search to find the story - and the mother - behind it. It was to take her seven years.

In 2006, after approaching everyone from hand-writing specialists and private detectives to psychic mediums and oceanographers, Karen was still no nearer finding the truth. It was then she decided to write a book about her quest.

The Letter in the Bottle was published in Britain in 2006, and in France in 2009, seven years after the bottle had been thrown into the sea.

Soon after its publication in France, Karen's luck changed and, finally, she tracked down and met the grieving mother, named as Marie (not her real name).

Marie told her story - her son Maurice had been killed one day in 1981 in a tragic accident.

In 2002, she had decided to write the letter, borne from her utter grief and despair and her anger at God for allowing his death to happen.

She had carefully selected the bottle, the ink, the ribbon - and had thrown the bottle into the sea from a cross-Channel ferry.

"I remember when Karen told me she had heard from her, it was just the most wonderful thing," said Sioux. "She genuinely didn't think anyone would ever find the bottle; it was symbolic, a cleansing process, an outpouring of her grief."

Sioux finally met Marie in France last year.

"I was so scared," she said. "But it was very moving and I cried straight away. I just wanted to hug her; I felt so proud of her because she had overcome this terrible thing.

"I was so grateful I could touch her and make sure she was all right."

But Sioux, chairman of Swale Arts Forum, said she did not know whether they would meet again.

"I don't know if this will ever close, but what has happened will stay with me all my life."

As for the bottle, London-based Karen still has it in her possession.

"She has become very attached to it," said Sioux, who runs Polkadot Art Centre, Teynham, with her partner Colin Barnard. "We did offer to give it back to the mother but we don't think she wants it back.

"It is not something I want to keep now that I know the story behind it. I really believe that one day it should go back to the sea - and that, you never know, might make another story."

• The Letter in the Bottle has been republished with a new chapter and postscript. It is available in paperback from Atlantic Books, price £7.99.