I am a postdoc, and with my former Ph.D. adviser have won a paper award which includes a sizable prize (10k+). I am the first author on the paper, and he is the second. The work is entirely mine, but he has been an excellent second author and mentor throughout this project and paper providing active feedback and many excellent suggestions along the way. Both of us will travel to the conference related to the award, and both of us already have our travel paid for by grants. At the conference, we will give a presentation talking about the background of the paper in which I will be the principal speaker. The question is this: how do we split the award, or do we split it at all?
Please note that this is similar to the following thread, but the roles have been changed somewhat: Share prize money from conference presentation award with co-authors?
Edit: thank you everyone for your excellent advice. I have sent an offer to split the prize, as you suggest.