Bear in mind that Louis and Marie Antoinette not being able to procreate was a serious political, not just private issue. Traditionally, such things led to marriages getting annulled, and the Austria/France alliance was pretty new and revolutionary, as Mildred explained above; there was a lot riding on it. Still, poor Antoinette who'd been 15 when marrying Louis, I think, and thus was only in her early 20s at the point where her mother must have decided she couldn't make heads or tails out of the ambassador's reports as to what the hell the problem was and needed to send brother Joseph to sort everyone out.

Which Joseph did, incidentally. (Not least because he realised there might be a medical issue and had a doctor perform an operation on Louis' penis.) Complete penetration, ejaculation, and subsequent procreation ensued. The other thing Joseph's visit to Paris was memorable for was leaving a Memorandum in which he told both his brother-in-law and his little sister that they needed to get some reforms going or else there was a road to disaster. This, famously, they did not listen to.