The 'Blurred Lines' hitmaker and his seven-year-old boy - whom he has with ex-wife Paula Patton - can both be seen lovingly looking at the tot, who was born on February 22.
Alongside the picture posted on Instagram on Tuesday (27.03.18), Robin - who has Mia with girlfriend April Love Geary - simply wrote: ''Lucky Daddy!''
The 41-year-old singer previously used Instagram to announce the birth of his daughter.
Robin shared a brief video of himself cradling the baby and wrote: ''On 2/22 at 13:33 Mia Love Thicke was born. Thank you God and April Love! (sic)''
Their little girl was born earlier than expected as when April, 23, revealed last August that she was pregnant, she told her followers that she was due to give birth on March 1, the birthday of Robin's late father Alan Thicke.
She shared a picture of her ultrasound scan and wrote: ''Robin and I are very excited to share with you all that we're having a baby! The due date is March 1st, Alan's birthday! (sic)''
The couple revealed last month they were planning to name their daughter Mia.
They shared photos from their baby shower, which took place on January 20, which showed a wall of flowers spelling out 'MIA', and the 41-year-old singer revealed his son had chosen the moniker.
He said: ''Julian came up with the name ... and I suggested the middle name Love after her mommy.''
In January, April revealed she had fallen pregnant during a vacation to Bali.
She posted two photos of herself and her partner, including one of him pointing at her stomach.
She captioned the images: ''This pic is 100000x funnier now because this Bali trip is when we made MIA [laughing emojis] little did we know a BABY was starting to grow in there!! LOL I love this man soooo much (sic)''
Meanwhile, Robin recently revealed Julian is showing signs he shares the same musical talent as his father and the youngster isn't shy about showing off his vocal talents.
He said: ''Oh god, Julian can sing already. The other day he was singing 'What A Wonderful World' in his end-of-school-year play. He just loves to sing and stand in front of everybody and hold the microphone and sing loud. He has a great voice.''