Natalie Portman insists she isn't as pregnant as she looks.

Natalie Portman

Natalie Portman

The 35-year-old actress - who already has five-year-old son Aleph with husband Benjamin Millepied - admitted people often assume she is just days away from giving birth because of the size of her bump, when in fact she still has several months to go.

She told talk show host Jimmy Fallon: "It's weird because I'm a small person in general, so you show a lot faster and a lot more when you're small.

"Everyone thinks I'm about to pop and about to give birth any minute, and I have months to go."

"I went to the store the other day to buy water and the guy at the checkout counter was like, 'Almost, huh?' I was like, 'No! Not at all!"

The 'Black Swan' actress had ran into the 42-year-old presenter in the summer at a time when she hadn't announced her pregnancy, but assumed people would guess her happy news because she was abstaining from alcohol.

However, Jimmy insisted she hadn't given anything away as he just assumed her "clean-living" ways were part of her lifestyle because she is vegan.

He said: "I just thought you were clean living, you know? I was like, 'Oh, that's Natalie, man. She rolls like that.' Because you're a vegan, right? So I was like, 'Wow, that's awesome.' I'm neither a vegan nor not drinking. I was so not pregnant.

"But this is unbelievable. This is great. Are people treating you differently?"

Meanwhile, Natalie - who is Jewish - is very excited about Christmas this year because her "secret wish" has always been to have a festive tree.

She said: "I celebrate Hanukkah; I'm Jewish. But my husband's family celebrates Christmas, so we usually do Hanukkah at ours and Christmas at theirs, but this year it's the same time, which is really nice. So, they're coming to us - to my parents.

"I was asking my husband, 'Is it OK if we don't have a tree?' And my parents are like, 'We can get a tree!' So excited!

"Like, my whole life - no Christmas tree. And then all of a sudden they have this great excuse, because it's kind of every Jew's secret wish to have a Christmas tree. It's so pretty!

"It's like, 'Why can't we have that, too?' It took 35 years to get here!"