Sacha Baron Cohen and Isla Fisher have named their son Montgomery Moses Brian Baron Cohen.

The couple - who also have two daughters together, Olive, seven, and Elula, four - welcomed their baby boy into the world on March 17, although they never announced he'd been born until Isla stepped out minus her baby bump last week.

Now, one month on, the name of the tot has been revealed thanks to TMZ who have obtained a copy of the birth certificate.

Before the 'Shopaholic' actress had given birth, a source had claimed her third pregnancy was the ''toughest yet''.

The insider previously said: ''Isla's exhausted. Sacha helps, but she's been finding this pregnancy her toughest yet because her daughters are so active.''

The 39-year-old actress had been convinced she was having a boy the whole time because she had been suffering from less morning sickness than her previous pregnancies.

The source added: ''Luckily, she hasn't had morning sickness this time and feels that could be a sign she's having a boy.''

Isla is also likely to be breastfeeding little Moses after she previously revealed she loved the special ''bond'' it created between her and her other children.

She said: ''What I loved about breast-feeding was that bond of one-on-one time. The serotonin that's released calms you down and connects you to the baby.''