Justin Timberlake's baby son's first word was ''dada.''

The 34-year-old singer believes five month old Silas, with whom he has with wife Jessica Biel, has bonded with him more than anyone else as the little one made reference to him when he uttered his first real phrase recently.

During an appearance on 'The Tonight Show Starring Jimmy Fallon' on Wednesday (09.09.15), the hunk revealed he'd coached his son using the presenter's new children's book, 'Your Baby's First Word Will Be Dada,' which follows the story of a father trying to coax his daughter into saying dada while meeting a number of animals during a fun adventure.

The 'Friends With Benefits' star has certainly taken to fatherhood and believes becoming a parent to his precious little boy has been the best thing to ever happen to him.

Asked how he would describe fatherhood, he said: ''It is the most insanely amazing, wonderful, unbelievable thing to ever happen to you.''

Meanwhile, although the Grammy-award winner is one of the world's best known singers, his wife Jessica previously revealed that she is on lullaby patrol for baby Silas because Justin doesn't want to bring his work home.

She said last month: ''You know, it's hard when it's your business. You don't always bring it home and use that as your casual time. I sing to the baby, poor thing. I do a lot of 'Somewhere Over the Rainbow'.''