Did Siddhartha Gautama achieve Nirvana?

Every book says that Siddhartha Gautama achieved Nirvana and then became Gautama Buddha. But now that I have realized that all phenomenon are nonself , it becomes imperative for me to ask : did Siddhartha Gautama achieve Nirvana? NOTE: It is not a duplicate of question "who or what achieves enlightenment?" because I am asking the question in relation to only and only Siddhartha Gautama. In the question "who or what achieves enlightenment?" Siddhartha Gautama is not mentioned and nobody answers for it.