According to Shoftim 5:27, per the explanation found in Yevamos 103a (in the name of רבי יוחנן), Yael had relations with Sisra.
אמר רבי יוחנן שבע בעילות בעל אותו רשע באותו היום שנאמר בין רגליה כרע נפל שכב בין רגליה כרע נפל באשר כרע שם נפל שדוד
R. Johanan Said: That profligate (Sisera) had seven sexual connections on that day; for it is said (Shoftim 5:27), Between her feet he sunk, he fell, he lay; at her feet he sunk, he fell; where he sunk there he fell down dead.
(Soncino translation)
Did she bear a son from these relations? If so, was he a prophet?