'La mia bella principessa' is the direct translation of 'my beautiful princess' in Italian. Another popular expression used to describe a love interest is 'La mia bella ragazza', which means my beautiful girl or girlfriend.
If you wish to find out the translation of other Italian phrases, you can always look into different ways to learn Italian. One popular method is to download a translating application to your mobile phone which will enable you to look up words and phrases as and when you wish to use them. You can also do this online, Google Translate is touted as reliable and fast, although both these methods require a working internet connection which might not always be to hand.
If you really want to impress your beautiful princess, why not consider learning some basic Italian? You can do this in so many ways that it can fit in with even the most hectic of lifestyles. One option would be to download a podcast, which are usually available inexpensively and will help you get a basic understanding of conversational Italian. Audio formats have the added benefit of being able to help you perfect your accent as some Italian phrases can be tricky to pronounce for the uninitiated.
If you're considering a tattooed tribute to your other half, you may find the phrase 'La mia bella principessa' a little lengthy. One alternative would be to use an abbreviation, with one of the most popular being TVTB which stands for 'Ti Voglio Tanto Bene' which is a way of saying 'I care for you so much' and is probably the most common form of graffiti seen on the desks of love-struck students in schools all across Italy.