Already in the early Christian communities, Mary mother of Jesus was thought of as a virgin. This dogma was confirmed by the Churchfathers, the influential writers that formed the Christian beliefs. Angel Gabriel told her she was pregnant, to which she replied how can that be? I never had any sex! Both Catholic and orthodox churches hold this for the truth though.
Then there were the brothers that are mentioned by Marcus in his book of the New Testament. Four of them are named in Marcus 6:3. For Catholics and Orthodox this is because the word nephew (adelphos) is the same as brother in the original Greek. So they are nephews, but most Protestant churches maintain that they’re brothers and that Mary consequently didn’t die a virgin.
Nobody’s contesting her relationship to Jesus though.