Justin Timberlake has discovered fatherhood is both "humiliating and humbling".

The star and his wife Jessica Biel became first-time parents to son Silas last year (15), and Justin admits he is still adapting to life as a dad, because every day is a new challenge.

"It changes everything," Justin told breakfast show Today. "You literally wake up and look in the mirror and go, 'I have no idea what I'm doing!'"

While he and Jessica are learning about parenthood as they go, Justin insists the actress has really come into her own as a mom, and watching her juggle her home life and work responsibilities is truly impressive.

The 35-year-old continued, "It's crazy. This new appreciation for both of them, her and him, it's humiliating and it's humbling at the same time... You watch her realize she has a gear she (thought she) didn't have and then you go, 'Woah, yeah.'"

Fatherhood has also influenced Justin's work in the recording studio, particularly on his summer (16) smash Can't Stop the Feeling!.

"I would have never written a song like Can't Stop the Feeling! (if I wasn't a father)," he added, although he didn't specifically write the tune with his boy in mind: "I don't know that it was directly inspired to be something that my son could listen to of mine, because there's a lot of music he can't... at least not yet... (but he was an influence)."

Timberlake penned the hit song for the soundtrack to his new animated film, Trolls, and he is also working on his fifth solo studio album, the follow-up to 2013's The 20/20 Experience.