The phrase "titular princess" refers to someone who holds the title of princess, but without the actual power or authority associated with it. They have the title in name only, rather than in practice. Full definition
She'd be coming aboard to work with fellow Brits in the form of actor / director Kenneth Branagh and titular princess Lily James, with Aussie Cate Blachett as the stepmom. (indiewire.com)
Do you remember in Pocahontas how whenever a big change was coming a wind would blow whimsical, multi-colored leaves around the titular princess and a magical tree would sing and she'd instinctively know that colonizers were coming, or that it was time to say goodbye, or how to speak English? (romper.com)
This film is also scheduled for a 2014 release, and stars Lily James as the titular princess. (allgeektome.net)