Carrie Underwood

Underwood is now a best-selling author.

It's Underwood's birthday and she's getting lots of love from her husband and boys!

Who is the fittest of the fit? When Underwood stopped by the "Tonight Show," Fallon offered up a challenge she couldn't resist.

No time to exercise? Underwood has a solution in the form of an app that offers effective 30-minute workouts.

Her boys are OK, but the city was hit hard.

What an amazing birthday party!

The singer posted a sweet tribute on social media to her funny, caring little Isaiah, who is growing up so fast!

Underwood wrote the majority of her book between 2AM and 5AM, she says.

They REALLY want to do this.

She had no idea what she was doing.