-je is a Dutch diminutive suffix used to create diminutive forms of names.
It derives from the Germanic diminutive suffixes -ka/-ko which merged with another Germanic diminutive -īn and became -kīn in Old Dutch and -kijn in Middle Dutch. In the 13th and 14th century it changed to modern -je.
Dutch and Frisian variant forms include -etje, -kje, -pje, -tje, -tjen.
See also -chen (German) and -ken/-ke (Frisian and Low German).