A Watford teacher who came out as gay at a school assembly has become world famous after a pupil emailed him a heartfelt letter of thanks - which gained millions of views on social media and a phone call from the Ellen DeGeneres Show in America.

David Weston, who started his career in teaching at Watford Boys Grammar School in 2003, battled through a potentially fatal liver illness and after a life saving transplant decided he wanted to address the school with an assembly about what it means to be gay, the law and homophobia.

During the assembly in 2010, Mr Weston, who was born and raised in Nascot, came out as gay and announced his engagement to his now civil partner.

Now, four years later, he received an email out of the blue from a pupil who was in that assembly.

Richard Miah wrote: "I just wanted you to know how inspirational your assembly was, and how much of a positive impact it had on the school...

"I know this message may seem a little pointless but I really felt you should know that you challenged the ignorance of so many people that day, and if every gay teacher shared your courage, then the world would be a much better place - not just for gay men, but for all of us. For that I thank you."

The 34-year-old posted the letter on social media and was shocked by the response.

He said: "Within 15 minutes it had more than 100 retweets. ITV got in touch, then BBC news and 5Live, newspapers - I’ve been blown away by the response. It’s had nearly 10,000 retweets and favourites and it’s been posted on facebook pages and got more than 40,000 likes, on one facebook page it was seen by 1.7million people.

"It’s been amazing, someone from the Ellen DeGeneres Show in America got in touch to say they thought it was brilliant what was happening and that they wanted to do a blogpost on it."

Mr Weston said he realised after his surgery that being a teacher meant being a role model and that he wanted to be open about his sexuality if anybody asked.

Mr Weston, himself a former pupil at Watford Boys Grammar School, said: "I was given a second chance. I thought that if family, colleagues, friends - if everyone knew someone gay no-one would need to be afraid. I was quite emotional - it was something I had to do.

"When you are a teacher, you’re a role model for your students. After I recovered I spoke to the headteacher, Martin Post, and said I’m gay and I want to be open about it if anyone asks. We talked about doing an assembly about homophobic language.

"It wasn’t designed as a coming out."

Mr Weston, who is now lives in Harrow and is chief executive of Teacher Development Trust, continued: "No-one should have to hide who they are at work. As teachers we are marking, preparing lessons - it’s relentless. But we are role models too and we have got to model being comfortable with ourselves, happy and confident to young people in our schools."