E. Phillips Oppenheim 
The Amazing Judgement [EPUB ebook] 

The world-weary Lord Hildyard, Marquis of Esholt, is on a yachting tour with a group of friends, including his kept lover, Pauline Owston. When Hildyard spies an apparently uninhabited island, he slips off the ship in search of adventure. What he finds is the exotic woman-child, Bertha, and her guardian, Stanley Owston, estranged husband of Pauline. Before the yachting party returns, Hildyard discovers himself in love with Bertha, and vows to return for her. But when the Owstons are dramatically reunited, Stanley confesses to his wife that Bertha is the daughter whom she has not seen in twelve years.