President Barack Obama, Ellen DeGeneres, Rosie O'Donnell and Lady Gaga were among the celebrities offering support for Caitlyn Jenner.

Earlier this year, Olympian and reality TV star Bruce Jenner came out as a transgender woman in an ABC News interview with Diane Sawyer.

Caitlyn Jenner debuted Monday in a preview of Vanity Fair's upcoming July cover story.

(Related: Caitlyn Jenner, formerly Bruce: Vanity Fair cover frees me.)

The story blew up on Twitter, where Jenner reached 1 million followers in only 4 hours and 3 minutes, a new record.

“It takes courage to share your story,” wrote Obama, the former record holder.

Ellen DeGeneres wrote: “My hope for the world is that we can all be as brave as @Caitlyn_Jenner.”

“She moves me so,” Rosie O'Donnell messaged.

Lady Gaga thanked Jenner for “being a part of all of our lives & using your platform to change people's minds.”

“The beauty on the inside is now also on the outside. God bless you and the whole family for sharing it with us,” she tweeted.