TT #681 · 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 / 39a.
TT lemma: וְיִבְּמָהּ.
שְׁנֵי אַחִים וּמֵת אֶחָד מֵהֶם וְיִבֵּם הַשֵּׁנִי אֶת אֵשֶׁת אָחִיו וְאַחַר כָּךְ נוֹלַד לָהֶם אָח וּמֵת הַמְּיַבֵּם – הָרִאשׁוֹנָה יוֹצֵאת מִשּׁוּם אֵשֶׁת אָחִיו שֶׁלֹּא הָיָה בְּעוֹלָמוֹ וְהַשְּׁנִיָּה מִשּׁוּם צָרָתָהּ.
English: Two brothers, one dies, the second performs yibbum, then a third brother is born and the yavam dies — the first woman is released because she is the wife of a brother who was never in his (the newborn’s) world, and the second (the yavam’s original wife) is released as her co-wife.
On the daf / in context: The residual designation “yevamah” after yibbum allows the later-born brother to be treated as never having shared the world with the original deceased.
Derash on residual yevamah status after yibbum.
A brother born after yibbum has been performed is not subject to yibbum with the original widow or her co-wives from the yavam.