Blake Lively was stunned when mistakenly thought a reporter complimented her ''t*ts''.

The 31-year-old actress - who has daughters James, three, and Ines, 23 months, with husband Ryan Reynolds - wore a revealing black shirt under a Givenchy suit to the New York premiere of her movie 'A Simple Favor' and she admonished a man on the red carpet when she thought he was commenting on her assets being visible through her top.

She told talk show host Jimmy Fallon she heard: ''Your t*ts are amazing!''

She added: ''I'm like, what? Are we saying that? Have you been on Google in the past year? This is not OK.''

But after a few minutes of confusion, the reporter added: ''And your husband's tweets are even better!''

Blake laughed: ''And I'm like, 'Oh, tweets! Twitter!' ''

But the 'Shallows' star joked she was then disappointed after finally understanding the comments.

She quipped: ''I was so relieved it was about my mind, and then after I was like, 'But how [is my chest]...How are they?'''

Blake admitted she was self-conscious about her red carpet outfit because she had no idea it was so revealing until she stepped out.

She said: ''It's actually a men's suit, believe it or not. But what nobody really realises, see the look of horror on my face?

''I didn't realise it was see-through, the shirt. That's not a look I was going for. Because it's a men's shirt!

''You know when you're freaking out about something and you know that's all anyone else is seeing?

''You know, you're aware of it, so everything everyone says is pointing out this thing you're paranoid about, but no one's really noticing.''