'Call me Caitlyn': Jenner debuts post-Bruce look

Lesbian, gay, bisexual and transgender campaigners -- and many well-wishers -- welcomed the high-profile proclamation, as did 65-year-old Jenner's family, including the media-savvy celebrity Kardashian clan.

"I'm so happy after such a long struggle to be living my true self," Jenner wrote in her first tweet after the magazine released the picture by renowned photographer Annie Leibovitz.

"Welcome to the world Caitlyn. Can't wait for you to get to know her/me," added Jenner, who sported a cream-colored strapless bodysuit and long brown hair for Vanity Fair's July issue.

In a video clip of the photo shoot on the magazine's website, Jenner said: "Bruce always had to tell a lie. He was always living that lie. Every day, he always had a secret, from morning till night.

"Caitlyn doesn't have any secrets," said Jenner, a reality television star, who is also shown in a black evening gown in the video.

"As soon as the Vanity Fair cover comes out, I am free," she said.

"Caitlyn Jenner" and the hashtag #CallMeCaitlyn quickly rocketed to the top of the Twitterverse as the top trending topic in the United States and worldwide.

Jenner's Twitter feed scooped up over half a million followers within less than two hours of her first tweet.

Jenner was widely praised for revealing in a television interview broadcast in April that she was transitioning to life as a woman, earning praise for coming out as transgender.

Monday's Vanity Fair cover was hailed by LGBT groups.

"By sharing her journey with the world, Caitlyn Jenner is accelerating acceptance of transgender people everywhere and reminds us all how important it is to live as your most authentic self," GLAAD head Sarah Kate Ellis said.

"For a transgender person to step into the world as his or her authentic self is a moment of tremendous freedom," said Nick Adams, GLAAD's Director of Programs, Transgender Media.

"The world can now see what Caitlyn Jenner has always known, that she is -- and always has been -- a woman."

Jenner's family also quickly rallied round on Twitter.

"How beautiful! Be happy, be proud, live life YOUR way!" wrote Kim Kardashian, Jenner's step-daughter and fellow reality television star.

Jenner became an American sports hero by setting a world record in the decathlon in the 1976 Olympics.

But it was through a previous marriage to Kris Kardashian that Jenner once again became a household name with the reality TV series "Keeping Up with the Kardashians," appearing as the sometimes bemused stepfather of her flamboyant daughters.

The couple married in 1991 and have two daughters together, Kendall and Kylie. They recently divorced.

Kendall Jenner wrote on Twitter Monday: "Be free now pretty bird."

Khloe Kardashian, Jenner's step-daughter along with Kim, wrote on Instagram: "We were given this life because you were strong enough to live it! I couldn't be prouder!!!