Natalie Portman's Baby Name Revealed
07/06/2011 AT 03:00 PM EDT
Their son's name is Aleph, a source confirms to PEOPLE.
So what's in a name? Aleph is the first letter of the Hebrew alphabet, much like alpha is the first letter of the Greek alphabet. Aleph is the number 1 in Hebrew and can also be spelled "alef."
Its esoteric meaning in Judaic Kabbalah, as denoted in the theological treaty Sefer-ha-Bahir, relates to the origin of the universe, the "primordial one that contains all numbers."
Portman, 30, met choreographer Millepied on the set of Black Swan, for which she later won an Oscar for Best Actress.
Reporting by JOEY BARTOLOMEO