Shounen Oujo

This Kingdom is complacent enough that the ruler is a queen and even she didn't notice Al's birth? Just letting the child be spirited away by the midwife while she's passed out? If the court required proof of childbirth than there would have been a whole host of royalty in the room watching the birthing so no kind of funny business like that could happen.

Nope, if Al returns with a baby that's obviously royal blood, that sword that's proof of lineage and an army after the country has been ravaged by social upheaval and war for long enough - I'm betting even the aunt that kept trying to kill him will welcome him back with open arms and closed eyes.

And to top it all off, now Al does have his friend Theo to rely on - there's no reason that Theo can't play "papa" and his female friend do the birthing, so Al can take them both home later as proof against the need for any other heirs.

Thats a good idea, but wouldn't people be demanding proof of some sort?
Proof that that the kid is 'hers', but more importantly proof that he is Alexia and not an imposter,
and the fact that he actually is one could make that complicated....