"One's long lost father" refers to a person's biological father who has been separated or lost touch with them for a significant amount of time. Full definition
He does the ultimate betrayal to her while Mitch's long lost father betrays him even more. (goodreads.com)
Karen's life as a small town receptionist is turned upside down when her long lost father she calls for a refrigerator repair. (metacritic.com)
After he befriends a tough street teen (Maisie Williams), he helps her construct the raft she'll use to sail across the Atlantic in search of her long lost father. (shockya.com)