Praise be to Allaah.
If they were alone together (khulwah) at the time when both of them were adults, then he has to repent, because being alone with a non-mahram woman and accompanying her here and there is a haraam action which is not permitted, as it opens the door to fitnah (temptation).
But if the man who accompanied her was a minor, so that there was no risk of fitnah, or if he was her mahram, or his accompanying her did not involve their being alone together, and she observed complete hijaab and so on, then he should state that clearly (to whoever he meets) so that he will not be accused. The Muslim should always ensure that his religious commitment and honour are above reproach. And Allaah is the One Whose help we seek.
Sheikh Muhammed Salih Al-Munajjid