Jessica Biel says she is "the luckiest human" to be married to Justin Timberlake.

Justin Timberlake and Jessica Biel (c) Instagram

Justin Timberlake and Jessica Biel (c) Instagram

The 36-year-old actress - who has three-year-old son Silas with the 'Suits & Tie' hitmaker - marked her spouse's 38th birthday (31.01.19) by posting a throwback picture of the couple underwater on Instagram, and admitted she doesn't mind having "smile lines", which she quipped are caused by her husband's jokes, because he fills her with so much "joy and laughter".

Alongside the snap, she wrote: "Since the days of embarrassing pink ruffled bikinis and underwater photo shoots, you have been infusing my life with so much joy and laughter that I blame YOU for my smile lines.

"But I wouldn't trade them for the world. I wear them with pride knowing that I am the luckiest human around to have the honor of hearing your jokes, your words, your voice, ever day of my life. (sic)"

Justin spent his birthday performing at Madison Square Gardens in New York, for his rescheduled 'Man of the Woods Tour' date - which he was forced to pull out of after damaging his vocal chords.

The night before his birthday, Justin shared a video of Jessica asleep and jokingly sang happy birthday to himself.

She then woke up and laughed: "I'm just preparing for our big night out. Just preparing."

He captioned the humorous clip: "Gotta work tomorrow for my bday so wifey really going all out tonight."

Earlier this month, the 'Total Recall' star heaped praise on the 'Say Something' hitmaker - who she tied the knot with in 2012 - for keeping their family together.

She said: "We're constantly reading each other's lines for auditions but honestly, this man held my family together.

"He held our family together. Without you, I would probably be divorced and sad and pitiful. I really do appreciate it is all I'm saying."