The photo, which was taken during the trio's visit to Paris, sees the 22-year-old perching on a rail from the balcony of his hotel room in front of a breathtaking backdrop showing the sun setting on the city's skyline.
Keely captioned the picture: "Paris in Paris. Photo by @piercebrosnanofficial @paris.brosnan #proudmama."
While most fans were loving the new vacation snap, one was left a little concerned about Paris' position on the balcony and worried that he was sitting a little too close to the edge of the railing.
The fan joked: "Lovely photo but every part of me is doing my mum thing, get away from the edge," adding a laughing emoji. Another follower commented: "True!!"
Other fans also took to the comments section to praise the idyllic snap, with one person writing: "WOW what a sunset. Great photo," while another commented on the striking resemblance between Paris and his parents: "You have a beautiful family @keelyshayebrosnan what a photo. The sunset looks like a painting and @paris.brosnan looks so much like his father and you."
Pierce also shared a photo on Instagram to mark the trio's trip to Europe. Sharing two photos of the James Bond star posing alongside his son in front of the Arno River in Florence, he revealed that the family also stopped off in Italy. The caption read: "Papa and Paris, Florence, Ponte Vecchio."
Fans were quick to comment on the photos, with one person writing: "Wonderful place, nice photos. Enjoy the time together," while another added: "Beautiful shot."
As well as 22-year-old Paris, Pierce and Keely also share another son, 26-year-old Dylan. Both sons have inherited their father's artistic flare, with Paris carving out a career as an artist, while Dylan has found his niche in music and modeling.
Admitting that his painting style differs quite dramatically from his father's, Paris said: "Our painting sessions are different. Mine is a little bit more chaotic, and Dad is calm, cool and collected."
Explaining that they often did enjoy painting together in their garage and giving each other feedback, Paris went on: "I'm like blasting music and throwing paint around, but when we are together, we rub off on each other. He inspires me to be more thoughtful and be more meditative while I inspire him to be more spontaneous and free flowing," he continued.
"He paints best when he's not overthinking it and just putting the emotion down. He's my biggest art inspiration, honestly."
Pierce's exhibition, titled "So Many Dreams," was followed by a poignant short film in which the Hollywood actor opened up about his upbringing in Southern Ireland, describing himself as "alone, somewhat, I was an only child. But I grew up in my imagination."
The film, which shared a glimpse inside look into his studio while he was at work on his canvas, was produced by Dylan.
Who are Pierce's other children?
Pierce is also a father to three other children. The Mamma Mia star has a son with his late first wife Cassandra Harris, whom he married in December 1980, named Sean.
Sean was born on 13 September 1983 and later followed in his father's footsteps in becoming an actor before finding his new passion as a counselor. Sean shares two children with his wife, Sanja Banic; Marley, who was born in 2015, and a baby boy called Jaxxon, who was welcomed to the world in November last year. Pierce has two older grandchildren called Isabella, 24, and Lucas, 17, via his late daughter Charlotte.
Pierce adopted Chris and his sister Charlotte – Cassandra's children – following the death of their father Dermot in 1986.
Tragically, both Cassandra and her daughter Charlotte passed away from ovarian cancer; Cassandra lost her life at the age of 43 in 1991, while Charlotte died in 2013 aged 41.
Read more HELLO! US stories here.