Not allowed to invite a goy to a yom tov seuda, according to Rabbi S.B. Cohen’s sefer on the laws of yom tov.
If he comes without being invited, it’s OK because you won’t feel obligated to prepare anything special for him.
The Shulchan Aruch (512:1) rules that one may not invite a gentile to one’s home for a Yom Tov meal. Although Halacha allows cooking on Yom Tov, one may cook on Yom Tov only for Jews; it is forbidden to cook food on Yom Tov for gentiles. The Sages therefore forbade inviting a gentile to one’s home for a Yom Tov meal, as he might then prepare food for him in violation of Halacha. Whoever says otherwise is arguing on the Shulchan Aruch.