Four years ago, teacher David Weston took a brave decision. Until that day he had been hiding a secret - a big secret - about his life.

In 2010, David decided to reveal he was gay. Not just to those he worked with at Watford Grammar, but to the entire school, staff and pupils, during morning assembly.

It was clearly a day David would never forget. And it was day the dozens of pupils wouldn't forget either.

For one pupil in particular the courage David showed that day inspired him so much that four years on, he sent this email thanking him for:

... challenging the ignorance of so many people. Former pupil, Watford Grammar

Here's the email in full:

David came out after an operation for a liver transplant. He left his career in teaching and set up a charity, the Teacher Development Trust which helps children succeed in life.

Hear David's story - in his own words - tonight on ITV London from 6pm.