Politician, actor and LGBT+ activist, Michael Cashman CBE said the fact that transgender people face discrimination from some others within the LGBT+ community is "unforgivable".
He said that it is important that LGBT+ people stand up to the injustices trans people are subjected to because "if you allow it to happen to others, then your own history will repeat itself".
He made the statements in an interview with the Welsh Government minister and MS for Neath Jeremy Miles, as part of this week's Pride Cymru events.
The full interview will be streamed online by Pride Cymru on Monday 24 August.
Michael Cashman is known for playing the role of Colin Russell in Eastenders, where in 1989 his character was one of those involved in the first gay kiss in a British soap opera. Mr Cashman is also one of the founders of the UK LGBT+ charity, Stonewall.
Mr Cashman compared the "misrepresentation" and "defamation" that lesbians and gay people faced in the 1980s to the same way transgender people are treated now.
Gay people were treated with "hatred" by the tabloid media during that time, according to Mr Cashman.
He said that it is "unforgivable" that some of the discrimination transgender people face now comes from other LGBT+ people themselves.
Speaking about how he became involved in activism, Mr Cashman said he came from a background where "if you saw an injustice and it affected you, it connected with you, you couldn't do or say nothing".
He said that when Section 28 - a legal clause that banned local authorities from "promoting homosexuality" or schools teaching "the acceptability of homosexuality as a pretended family relationship" - came in in 1988, he knew he had to speak out or he would not be able to look at himself in a mirror.
There come moments in your life where if you don't accept them, then it's lost, there isn't another opportunity.
Following mass protests and campaigning, Section 28 was repealed in Scotland in 2000 and the rest of the UK in 2003.
Mr Cashman added that being on Eastenders and portraying a gay character paved the way for him to get involved with things like campaigning against Section 28 and forming Stonewall.
Interviewer, Jeremy Miles revealed: "I was in my teens at the time and I knew I was gay, and I've got to say to you that the relationship between Colin and Barry in Eastenders became for me and I'm sure for thousands of others, a signal, a public signal really of the kind of affirmation of your identity as a gay teenager in my case and to see on prime time television, on the BBC, a gay relationship being lived out on screen was incredibly validating."
The actor turned activist also described how one of his most significant moments during his 15 years in the European Parliament was when he helped to stop a 17-year-old gay Iranian from being deported from the UK.
The young man would have been sent back to Iran where he faced being killed because of his sexuality.
Mr Cashman said: "To be able to have played a tiny part in that, is a privilege that will rest with me for the rest of my life."