Ellen DeGeneres admits revealing her sexuality on TV was the "hardest thing" she's ever done.

Ellen DeGeneres

Ellen DeGeneres

The 59-year-old talk show host - who is married to Portia De Rossi - is celebrating the 20th anniversary of her sitcom 'Ellen's famous coming out episode and though she admits publicly declaring her own attraction to women was tough, she doesn't ever regret it.

In an Instagram video, she shared a teaser of her monologue for Friday's (28.04.17) episode of her talk show, in which she fought back tears as she said: "You are here on a very special day. Today we're celebrating the 20th anniversary of the coming-out episode of my sitcom.

"It was the hardest thing that I ever had to do in my life and I would not change one moment of it because it led me to be exactly where I am today standing in front of all of you."

And a clip from the opening moments of the show saw Ellen said: "I'm Ellen and I'm gay. 20 years ago I said that -- it was a much bigger deal then."

When Ellen and her character on the show came out on April 30, 1997, it was done in scenes taped in front of a live audience, and the blonde star has now explained why the iconic moment was called 'The Puppy Episode'.

She joked: "It was called 'The Puppy Episode' because we wanted to keep it a secret until it aired and because 'Ellen Throws Her Career Away' seemed too on the nose."

She then added: "Actually, the real reason we called it 'The Puppy Episode' is because when the writers told the executives that they wanted me to come out, because my character needed to be in a relationship after four years of not being in a relationship, someone at the studio said, 'Well, get her a puppy. She's not coming out.' "

In the episode, Laura Dern played openly gay Susan, who enlightened Ellen to her own sexual identity, and the actress was thankful to be a part of the key moment.

Speaking on Friday's show, she said: "It was so profound and I feel so blessed that I got to be there and witness that."

Oprah Winfrey is another guest on the show, and the preview showed her praising Ellen for her bravery.

She said: "You wouldn't have been able to open hearts and touch hearts and change people's minds and make a difference in the world had you not had the courage to do that."