Mori V'Rabi Harav Hagaon R. Shlomo Miller shlita told us during Shiur, today:
"Someone asked him a Shailo and he answered him that it is Mutar.
The Shoel (questioner) wasn't satisfied with the answerand felt to be Machmir (stringent) would be more appropriate."
Reb Shlomo told him
"Ploni Almoni (Tov) because he wanted to be Machmir not to marry Rus missed the opportunity of becoming the grandfather of Dovid Hamelech and Melech Hamashiach."