Yes. Granted my sibling and I are clearly from the exact same progeny, it’s totally obvious. If you aren’t sure as a mother or father, I think it’s your responsibility to air that out at a point that you feel (your discretion) your child is ready to know, regardless of the affects that might have on your marriage. A child needs to know from a genotype standpoint what he/she can reasonably expect, what to avoid, what might work well, etc. Phenotype can change dramatically based on environment(ex. I was born with blue eyes and extremely blonde hair, eyes didn’t change till I was 3, hair at 7-10, now it’s all brown with a heterochromia defect, one eye is a light brown, one is totally dark brown), if you’ve provided a decent one for your child, I wouldn’t worry that “seeing” their biological whatever is going to cause a lasting problem. Another factor could be how much the estranged parent knows about their likely genetic defects as determined by their relational health history. But, all of this could be completed with a DNA test costing less then 1k, and be much more comprehensive and accurate. It’s sort of a null point.