Justin Timberlake and Jessica Biel's son is "growing up" fast and has just started school.

Justin Timberlake and Jessica Biel

Justin Timberlake and Jessica Biel

The superstar couple's three-year-old boy Silas is getting "big" now, and the proud parents are delighted to be ticking off another milestone in his development.

Speaking to 'Extra', Jessica revealed: "He's sooo good, sooo big -- he started school today, pre- pre-K... it's a big deal...

"He's just getting so big and so funny. He has beautiful long hair that we haven't cut yet. He's just growing up."

The loved-up pair - who got married in 2012 after dating for five years - recently took a family trip to Italy, with Jessica, 36, admitting the European country is their "happy place".

Her 37-year-old husband added: "If you don't have fun in Italy, there's something wrong with you."

Although their busy globe-trotting careers often separate them, the actors believe their marriage is solid because they work hard to keep the peace and understand one another.

The brunette beauty recently said: "We're lucky enough to go and stay in different places and live in different places while we work and that's definitely part [of having a strong marriage].

"But, honestly, I just really feel like you have to work hard. That doesn't change if you work at home or in an office or you're on a tour. It doesn't change, the work doesn't change. Being devoted to the relationship is our biggest priority."

Despite trying to make time for date nights while Justin is on the road touring, Jessica has admitted they tend to opt for cosy time in the hotel room.

She explained: "Yes, we're in these amazing places, but a lot of times we're trying to protect his immunity and protect his body from breaking down.

"A date night for us would be just sitting in the hotel and having room service and watching a movie -- just like everybody else."

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