The singer and wife Jessica Biel secretly welcomed the tot last summer.
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Baby Phineas has made his social media debut - a rite of passage for any celebrity offspring (up there with first steps and words). 

Justin Timberlake and Jessica Biel's 11-month-old son, aka their "secret COVID baby," casually appeared on the singer's Instagram gallery in honor of Father's Day this past Sunday.

"Being a dad is better than I ever could have imagined," Timberlake began. "Thankful to my dads and my grandfathers for leading the way, making the sacrifices for me to live out my dreams, and for teaching me that REAL LIFE happens in all the little moments. Happy Father's Day to all the dads out there!!!"

The father of two's post included an image of himself with his and Biel's 6-year-old son, Silas, as well as one of the three Timberlake boys - Phineas plopped down on the carpet while both sons appeared to play a video game with their dad. 

Phineas's birth came as a surprise when it was announced last August. Biel's pregnancy had gone completely unreported. 

"It wasn't like it was supposed to be a secret," Biel told Dax Shepard during an episode of his Armchair Expert podcast last week. "It was just COVID happened, and then I went to Montana with my family and never left."