This is a sure sign that the interviewer likes you and is already thinking about contacting your previous employer for a reference. And this is the time when you realise how important it is to choose your referees carefully. So answer this question in the way that you would like to think your employer would respond.

For example:

I have an excellent working relationship with my manager and we have mutual respect for each other. He considers me to be hard working, dedicated, reliable and able to work well using my own initiative.