But the Oscar winner is now showing off his cute little mug in Los Angeles.
And what a face it is!
So where were they headed?
The Black Swan star, dressed casually in cutoff jeans and sneakers, and her boy, rocking a neon green onesie, met up with a female friend for a stroll.
After baby Aleph spent some time peering around with his big adorable eyes, the actress did attempt to cover his head with a blanket, which didn't stay on.
Natalie's ballet-dancing baby daddy, Benjamin Millepied, was nowhere to be seen, but the duo are going strong, having just returned from a family trip to Paris with the baby.
The new mom, who calls looking after Aleph her "most important role to date," has not yet signed on to any post-baby acting roles.