The Catholic church contends that Mary, the mother of Jesus, was an eternal virgin.  This belief is not supported by scripture and wasn't introduced until more than 400 years after the time of Christ by a Catholic priest by the name Eusebius Sophronius Hieronymus, also known as Jerome (c. 347–420). Scripture clearly shows that Mary did NOT remain a virgin and that Jesus had brothers and sisters.  Consider the following.
If someone tells you they did not like Ford automobiles until they drove one, what is implied by the word "until"?  Of course, it means that after they drove a Ford, they liked them.  The statement was true "until" something happened.  It then changed.
If, as a child, your mother tells you that you cannot have dessert until you've eaten all your vegetables, what do you conclude?  You know that means you WILL be able to have dessert after you've eaten your vegetables.  No one thinks otherwise.  The forgone conclusion is always that the situation changes after the "until" happens.
The Bible tells us in Matthew 1:25 that Joseph did not have relations with Mary until "after she brought forth her firstborn son."   That word again - -UNTIL !!  What is the conclusion?  Without question, just as with the preceding examples, things changed after "until" happened.  There is no doubt that Joseph DID have relations with Mary after her son was born.
It's incomprehensible that anyone would say Mary remained a virgin after Jesus was born and that Jesus did not have siblings.  The Bible affirms numerous times that He DID have siblings.  His mother and "brethren" are referred to several times (Matthew 12:46, Luke 8:19, Mark 3:31 and Acts 1:14).  In Matthew 13:54-54 at least four of his brothers are named (James, Joses, Simon, and Judas) and His sisters (plural) are mentioned.  So Mary had AT LEAST 7 children - Jesus, four brothers and two sisters.  Perhaps more.
The Catholic church desperately defends their belief in Mary's virginity by dancing around the meaning of the word for "brethren", saying it simply means "relative" or "cousin".  They carefully avoid the fact that the word is also used to indicate just what it says, "brethren".  To admit that the word means the literal "brothers" of Jesus would invalidate their claim about Mary, yet it is perfectly consistent with other scriptures speaking on the subject. 
There is a final point regarding the false claim that Mary remained a virgin.   If you have only one child do you ever introduce that child to people as your first born? Of course not !  If you have several children, you may very well introduce your oldest as your "firstborn", but you would never use that term for an only child.  Jesus is referred to as Mary's "firstborn", leaving no doubt that she had other children.  Jesus was the FIRST child born to Mary.
To suggest that Mary was an eternal virgin is in complete opposition to what God's Word tells us.