Will you get HIV from someone that is positive from putting the shaft in one time without a condom?

If someone that is HIV Positive get caught in the moment of being intimate with a partner, and they put their inside without a condom for like 5 seconds before they caught them self to get a condom...how high is the risk of getting the HIV. The guy that has it, says he has had it for years but with treatment and his genotype is now undetectable.