In one particular episode, one of the actors accidentally refers to Doug Heffernan (of King of Queens, as played by Kevin James) as "Kevin" - his real life name. Kevin James appeared 9 times in "Everybody Loves Raymond." In the first six appearances, during seasons one and two, his character was simply referred to as "Kevin." In the final three appearances, during season three, he portrayed his "Doug Heffernan" character from "The King of Queens." This is probably because the final appearance as "Kevin" took place in May of 1998, while "The King of Queens" did not debut until September of 1998.
