There would be no capital gains to pay on the transfer to your son or back to you, quite simply because there is no capital gain. Tax situation on the eventual sale however to any third party, just like the other properties, is that Capital Gains Tax would then be payable in exactly the same way as it was on the others which you sold.
Can I clarify anything for you? Please rate the service positive so that I get paid. We can still exchange emails. Best wishes. FES.