Image copyright Cardiff University Image caption Prof Riordan said he "I felt uncomfortable that people presumed I was straight"

When Cardiff University's vice chancellor prepared to send his monthly email to staff, his finger hovered over the send button for just a moment longer than usual.

For alongside his usual round-up of academic affairs and campus matters, Prof Colin Riordan also included a personal note explaining he is bisexual.

His unorthodox memo explained how he had completely missed the university's bi-visibility day, held on September 23, despite a colourful 'bi' flag being raised above his very building.

"This seemed a pity," he wrote, "because I count myself in that category and I wondered how this could all have passed me by.

"Rather obviously, it was probably because people didn't know I would identify as bi and so I thought - if this is about visibility - that it might help if I did."

Explaining his decision to speak out, Prof Riordan said, "I felt it important to say I had noticed bi-visibility day and been encouraged by it.

"I wanted to show it was a good thing, to help stop making bisexual people feel invisible."

'Felt fraudulent'

But it was a move which might perhaps have surprised his 7,000 staff, including close colleagues.

Prof Riordan said that, despite having held his Cardiff post for five years, he had not told anyone at work, nor in his previous role as vice chancellor of the University of Essex.

"I never deliberately kept it a secret but I never felt the need to mention it either," he said.

"Obviously, anyone I was in a relationship with knew the situation, but there was no real reason for colleagues to know."

But this led to a situation where some at the university presumed he was "straight" - something which weighed on his mind.

Prof Riordan added: "When I joined Cardiff University, I was asked to become a friend of Enfys - the university's LGBT network - but then I read an article somewhere where I was described as its 'straight friend'.

"I felt fraudulent and uncomfortable that people presumed I was straight. Speaking out allowed me to correct the false impression."

Image copyright Cardiff University Image caption The bi-visibility flag flying over Cardiff University on 23 September 2017

The move also allowed Prof Riordan to show support for the bisexual community, which he believes "still faces problems".

"Invisibility is a big problem for people who are bisexual, because they often have no need to mention it," he said.

"People would notice if the person was gay, but being bi is not so obvious, and that's why we should talk about it."

There are also stereotypes to contend with.

He added: "I've been told I'm gay and just in denial. I've also been told there is no such thing as bisexuality and also that everyone is bisexual to some degree, which is quite dismissive.

"I've never been accused of being promiscuous, but that can happen.

"Some people too can feel excluded by the LGBT community because they are not exclusively gay, though again, I've not encountered this.

"More often, people in this scene are just suspicious, like they are not quite sure what you're all about."

Despite these problems, however, the former German lecturer, 58, has never wished he was different.

He said: "I've never wished for anything else. I've always been this way and I've always been aware of it."

Image caption The bi-visibility flag is pink, lavender and blue

That said, speaking out about his bisexuality has not been easy.

"Making the decision to send the email to all those thousands of people was quite worrying and stressful," he said.

"Although this is not a big thing for me, I knew it would be seen as a big thing by others.

"It feels quite exposing, and I knew some people might react badly.

"I don't suppose I'd have done it had I not felt it to be so important."

Reaction to the news, however, has been nothing but positive - with staff emailing him to say it has helped give them courage and think about their own issues.

But perhaps most surprising of all, has been Prof Riordan's own relief.

He said: "Already I feel more myself and that a weight has been lifted. I am now being truly honest with those around me, and there is a certain freedom in that."

So, does he feel the time is right for people in powerful positions to be more open about their sexuality?

"Twenty years ago, I would never have mentioned this in the work place," he said.

"It was simply not spoken of.

"I realise that not everything is solved in terms of LGBT rights, but compared to how things used to be, there's a huge difference."

Image copyright Matthew Horwood Image caption Thousands of people head to Cardiff city centre each year to celebrate LGBT event, Pride Cymru

With his announcement, Prof Riordan, who has two grown-up daughters from a former marriage, joins a tiny minority of leading academics who are openly non-heterosexual.

He said: "Only a few vice chancellors have spoken out about being gay or lesbian and none about being bi, as far as I'm aware.

"People have said that I am brave for telling the truth, but I don't feel it.

"In all honesty, I think most people don't really care one way or the other.

"Cardiff University is already very progressive in terms of its support for LGBT people.

"But if there is a chance that any of our students or colleagues might feel more supported and less invisible by my mentioning this, then it's worth doing."