Hi and welcome Mykawa,
All you have to do is right click on the general character and then click on the helmet on the left side of his scroll. If it says "Late", "Armoured" or "Cavalry" in the bodyguard unit's name then it is definitely a reformed General's Guard. This is also a useful way of checking if the Romans have had their reforms yet, if they have had their reforms then your bodyguard will have had their reforms. Good luck with your new general's guards, cheers!