Liberal Democrat MP Layla Moran has announced she is pansexual and in a relationship with a woman.
The MP for Oxford West and Abingdon, who previously only had relationships with men, told PinkNews she is in a relationship with ex-Lib Dem press officer Rosy Cobb.
Pansexuality describes those who are attracted to a person regardless of their sex or gender.
"It's about the person themselves," said Ms Moran,
Speaking to the PinkNews website, Ms Moran - a potential candidate to become the next Lib Dem leader - also criticised Parliament as a "weird, backwards place" for LGBTQ people.
She said coming out in the context of being an MP had been "slightly more difficult" than telling her friends and family.
The MP also shared a picture of herself and Ms Cobb on Twitter, writing that she is now "just happy".
2020 is a new decade and a new path in my journey. Last year I fell in love with a wonderful woman. Something I’d never even considered before. Now I am just happy #Pansexual #OutAndProud pic.twitter.com/jdfz87Hdkx— Layla Moran 🔶 🏳️🌈 (@LaylaMoran) January 2, 2020
"It was really wonderful on the one hand, but also quite surprising for me in how I had identified before," she said.
"I feel now is the time to talk about it, because as an MP I spend a lot of my time defending our community and talking about our community. I want people to know I am part of our community as well."
She said her family and friends have been supportive, but some people had suggested being in a same-sex relationship could damage her career.
"They definitely would not have said anything like that had she been a man," she added.
"Parliament is a weird, backwards place. I don't know if there's any other (MPs) who would identify as pansexual, and not that many who identify as bisexual - there are a few women who are brilliant role models who have come out in their lesbian relationships."
'The person matters'
Ms Moran, who did not rule out running to take over as Lib Dem leader, was asked to describe pansexuality to someone who is not familiar with the term.
"Pansexuality, to me, means it doesn't matter about the physical attributions of the person you fall in love with, it's about the person themselves," she said.
"It doesn't matter if they're a man or a woman or gender non-conforming, it doesn't matter if they identify as gay or not.
"In the end, these are all things that don't matter - the thing that matters is the person, and that you love the person."
According to the charity the LGBT Foundation, pansexuality is different from bisexuality - but they are not mutually exclusive and some people identify as both.
"Being bisexual means being attracted to more than one gender, while being pansexual means being attracted to people regardless of gender," the foundation said.
"Pansexuality is included under the bisexual umbrella, which covers anyone who experiences sexual or romantic attraction to more than one gender."
Meanwhile, charity Stonewall says pansexual "refers to a person whose romantic and/or sexual attraction towards others is not limited by sex or gender" - and bisexual people may also describe themselves as pansexual.