Finn was born when Chris was a sperm donor for Carrie Burton. Carrie who went on to have triplets, including Finn's siblings Frank and Sarah.
Finn's close to his sister Sarah (Sass), although she's his polar opposite morally. He has a deeply loving, honest relationship with her.
The arrangement was that Chris would have no contact with his offspring, so Finn grew up in Australia.
He always thought of his step-dad, John Connelly, as his father. Carrie died recently and told the truth about her children's parentage before she passed.
This is why Finn came across the ditch to seek out Chris. Now Finn is a surgeon at Shortland Street, and has a good relationship with the Warners.