Several have mentioned the ability young girls have to 'trick' young men. Older ones do also.
My daughter is very anti-having babies without being emotionally and financially ready. She's been like this since her teens-when 2 of her friends fell pregnant just after doing their GCSE's. One girl kept the baby-and last I heard was an excellent young mum. The second girl had lost her own mum only a year before,and her dad worked away-effectively leaving her to fend for herself at 15. She did not keep the baby. But....she had a baby about 6 months ago-she had a brief 'fling' with a young man-got pregnant,and had no intention of including him in the 'family'...I heard that she was having second thoughts over that-but only for the financial contribution he might make. She may have to sell the 'dream' BMW she bought with the £££ her mum left to her.
Back to the Q-I think I'd initially be furious-like someone else said-'HOW-in this day and age?'...but then I'd know that giving love,support and advice would be my only option. Your son sounds sensible,Smowball...let's just hope the baby is his-it would be a shame to see him deceived-it would have a lasting effect on any future relationships for him.