George Takei "didn't like being different" when he was younger.
The 'Star Trek: The Original Series' actor - who officially came out in 2005 - admitted there was "no one point" when he realised he was gay, and his time in an imprisonment camp for Japanese Americans during World War II meant he didn't want to not be like his friends.
Speaking on 'David Tennant Does A Podcast With...', he said: "I knew from childhood that I looked different and for that we were punished. We were put into imprisonment.
"When I was about 9 or 10, I had the growing realisation that I was different in ways other than just the face.
"The other boys in junior high school, middle school, would get all excited. There was a girl named Monica who was prematurely blossoming out and they would say 'Woah, Monica is hot!'
"I thought, Monica's nice, but what are they getting so excited about? All the other guys felt that way, all my friends, and I didn't. I didn't like to be different because we were punished for being different."
George - who married his husband Brad Altman in 2008 - opened up about how he felt when he realised his own sexuality.
He added: "My difference was in the way I felt. When I saw Bobby, he has such a cute smile, and they didn't think so.
"There's no one point when you make that realisation. I'm different in other ways too. I didn't like being different.
"I was an actor from a very early age. You feel very alone. I thought I was the only one who had those feelings."
The 83-year-old star revealed while he was glad to have a place "where other guys like us gathered", there was an element of fear.
He said: "Then, as you grow older, you meet other guys who would tell me about this place where other guys like us gathered.
"We had to go in through the alleyway. On the street side, it's all painted black: the gay bar. I heard that's what they were called.
"One of the older guys told me that even in a gay bar you have to be careful because the police raided them, and they would arrest everybody, march you all out, and put you in a bandwagon, and take a picture of you, and put your name on a list."
'David Tennant Does A Podcast With... is available on Apple, Spotify and all podcast providers. A Somethin' Else and No Mystery production.