From mer- + prince.
merprince (plural merprinces)
- (fantasy) A merman who is a prince.
2003, Gretel Killeen, My Sister's a Sea Slug[1], Random House Children's Publishing UK, published 2012, →ISBN:We have the merprince and merprincess and tonight we will finish defeating the soldiers at the mercastle.
2005, Tracey V. Bateman, Kansas Home: Hearts Adrift Find a Place to Dwell in Four Romantic Stories, Barbour Publishing Incorporated, →ISBN, page 49:She sighed audibly when the merprince rescued the young mermaid and whisked her away to his kingdom as his bride, thus ending the story.
2005, Rachel Roberts, The Heart of Avalon, CDS Books, →ISBN, page 18:Down the beach, a group of mergirls and boys were facing off with the same merprince who'd spoken through the mirror.