A prominent Jewish mental health campaigner has described himself as “incredibly humbled” after it was announced that Prince William had written the foreword to his first book.

Kensington Palace tweeted that the prince had contributed the piece to Jonny Benjamin’s book, The Stranger on the Bridge: My Journey from Despair to Hope.

“Mental health is not a dirty word – we all have mental health like we do physical health, good or ill” the prince wrote.

“But I have seen time and again how not seeking help when it all seems too much can impact the rest of our lives.

“As you will read in this book, at times for Jonny it has been hard but thanks to a strong support network and his personal determination to get through, he provides an extraordinary example to us all.”

A further tweet from Kensington Palace described Prince William as praising Mr Benjamin's "bravery, passion and determination."

Mr Benjamin said he was “incredibly humbled and honoured” that Prince William “wrote such supportive and generous praise for The Stranger on the Bridge.

“The writing of the book has been both challenging and cathartic and l’m excited to see it on the bookshelves but, most importantly, l really hope it will inspire and help people who are experiencing any kind of mental health struggle.”

A decade ago, Mr Benjamin, who had been diagnosed with schizoaffective disorder — a form of schizophrenia — climbed over the railings on Waterloo Bridge, ready to throw himself off.

A passer-by stopped to talk to him and persuaded him not to take his life. Six years later, Mr Benjamin launched a campaign to find the man who had saved him. With national attention, it took just two days before the man in question – Neil Laybourn – made himself known.

Mr Benjamin received an MBE last year from Prince William for services to national campaigning on awareness of suicide and mental illness. An ambassador for Jami (the Jewish Association for Mental Illness), two years ago Mr Benjamin launched Thinkwell, a workshop designed for children between the ages of 13 and 18 in schools across the UK, intended to fill "the massive gap in the national curriculum when it comes to mental health".

Prince William concluded his foreword by saying: “On the several occasions we have met throughout the Royal Foundation's Heads Together campaign, I have been struck not only by Jonny’s sincerity and openness but his ability to show that a mental health diagnosis should not put limitations upon anyone.

“With Neil, I watched him run the London Marathon past that very same bridge where their journey began, and I know there is so much more on this journey to come.”

The Stranger on the Bridge is published by Bluebird on May 3.