TT #645 · Parashas Ki Seitzei · Seventh Aliyah · Passuk 25:05
When brothers dwell together and one of them dies and has no son, the wife of the dead shall not be outside to a strange man; her husband’s brother shall come upon her and take her to himself as a wife and perform the duty of a husband’s brother for her.
Torah Temimah points to Yevamot 17b.
TT lemma: כִּי יֵשְׁבוּ אַחִים יַחְדָּו.
אֵשֶׁת אָחִיו שֶׁלֹּא הָיָה בְּעוֹלָמוֹ פְּטוּרָה וּפוֹטֶרֶת צָרָתָהּ מִן הַחֲלִיצָה וּמִן הַיִּבּוּם, דַּאֲמַר קְרָא כִּי יֵשְׁבוּ אַחִים יַחְדָּו – שֶׁהָיְתָה לָהֶם יְשִׁיבָה אַחַת בָּעוֹלָם.
English: The wife of a brother who was never “in his world” is exempt and exempts her co-wife from chalitzah and yibbum, for Scripture says “When brothers dwell together” — implying that they had a simultaneous period of dwelling in the world.
On the daf / in context: A brother born after the death of the deceased is not considered to have “dwelled together” with him; therefore his yevamah is free.
Derash on the requirement of simultaneous existence.
A brother born after the death of the childless brother is not subject to yibbum or chalitzah with the widow.