White stuff during sex

Its not semen I think. The last time my SO and I had sex, he noticed white stuff at the base of his dick. It looked like discharge to me, but he said he had never seen that before. Sometimes he does come inside me, could  that just be some leftover semen from before? 
Discharge is pretty normal for me, but its never come out during sex like   that. 
Should I be concerned?

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