The Hollywood couple welcomed their third child on 17 March and, according to reports, the tot has been named Montgomery Moses Brian Baron Cohen.
TMZ claims to have uncovered the name through a birth certificate filed with the LA County Department of Public Health.
Isla and Sacha have not commented.
The incredibly private couple did not even publicly confirm the birth or sex of their third child. News that they'd welcomed a new member of their family came via sources in April.
Isla and Sacha are also parents to daughters Olive, seven, and Elula, four.
Check out some of the best maternity fashion below: