Participation in the Kiddush for Chatan Torah in the Synagogue during the Year of Mourning

Can a mourner within the year for his father participate in the Kiddush held for Chatan Torah and Chatan Bereshit, in a way that even if he does not participate, it will not be noticeable?

A mourner within the year can participate in the Kiddush for Chatan Torah and Chatan Bereshit, and even eat.

The Rema in Siman 669 writes: "It is customary that the one who completes the Torah and the one who begins Bereshit make vows and invite others to make a feast," and the Mishnah Berurah there, SK 8, writes in the name of Bikkurei Yaakov: "And even a mourner within twelve months can eat at this feast." It seems that his reasoning is that since it is a communal joy for the completion of the Torah, it is considered a seudat mitzvah even for the mourner, and he can participate in the Kiddush, even when not at home. Rabbi Avraham Palagi writes that a feast for the completion of the Torah is the greatest seudat mitzvah, and it is preferable to a feast for the completion of a tractate. Moreover, this joy is the joy of all Israel, not just for the Chatan Torah himself. And he can even eat, because if he does not eat, it will be mourning in public.