During his appearance on The Ellen DeGeneres show, the 39-year-old also revealed his son's unique name - Phineas.
"His name is Phineas, and he is awesome and so cute and nobody's sleeping but we are thrilled. We are thrilled and we couldn't be happier. We are grateful," he said.
WATCH: Justin Timberlake talks about his second son Phineas
Ask how he and Jessica are coping with two children, he joked: "We don't see each other anymore," before adding: "It's a lot of fun, but I guess the saying goes 'Go from a zone defence to a man-to-man very quickly'. It's great, and Silas is very excited. Right now he is very much liking it.
"Phin can't walk yet or chase him down, so we'll see what happens," he said.
The actor and singer then went on to reveal that his five-year-old is musical, just like him, but he enjoys other hobbies such as "Legos, tennis and we got him a Nintendo Switch... yeah... it's like child crack. Can I say that on daytime TV?"
The couple are parents to two sons, Silas and Phineas
Justin and Jessica, who married in 2012, welcomed their second son in July last year, following a top-secret pregnancy.
The happy news came seven months after the singer issued a public apology to his wife Jessica after being photographed holding hands with his co-star, Alisha Wainwright.
Back at the time, Justin shared a post on Instagram in which he acknowledged a "strong lapse in judgement".
Justin began: "I stay away from gossip as much as I can, but for my family, I feel it is important to address recent rumours that are hurting the people I love. A few weeks ago I displayed a strong lapse in judgement – but let me be clear – nothing happened between me and my co-star. I drank way too much that night and I regret my behaviour. I should have known better."