If there are berries, you have princesses, not princes!! While males are necessary for the fertilization, they cannot reproduce themselves, ergo no berries.

Where did you get said 'Prince/Princess'? If Home Depot (I've noticed they often tag their Blue hollies with 'Blue Prince/Blue Princess') , I wonder if they don't combine male-female plants in the same pot to assure a berry set. I bought one too and it does get a few berries, though not prolific. But as GardenGal said, if you're getting berries, that plant is female.

A closeup pic of the holly flowers would reveal whether they are male or female. Male holly flowers have a depression in the middle; whereas the female flowers have a green developing ovule/berry.

Holly trivia - just for added confusion the name is not always a guide to the sex with hollies. Bizarrely, Silver Queen is male and Golden King is female.

Fortunately with the Merserve holly hybrids, 'Blue Prince' and 'Blue Princess' names were intentionally used to indicate the sex, so that paired plants could be purchased to assure good berry set. They were released at the same time -- around 1972.

Similar with 'Blue Maid' and 'Blue Stallion'--another pair of hardy meserve hybrids.