It's in the chapter 133, it's "In this world, Grayfia and syrzechs never did that even though they have been married for many years."But in the earlier chapters, it's okay there is no mention of her being a virgin.

Didn’t you make Grayfia a virgin before ?Isn't that the reason why she didn't have a son anymore ?You need to either change the previous chapters mentioning she was a virgin or change this one.