代词不是不倒装吗？为何下句中主句倒转了？

Not only does he know him,but also they are good friends.他不仅认识他，而且他们是好朋友。not only but also不仅而且，I can not only play the flute but also play basketball.我不仅能吹笛子，还能打篮球。但是放在句首，否定词not放在句首，就需要倒装，提前的是助动词dose，没有提前代词，正常语序是He knows him.他认识他。