In divorce, What is buying price of a property when calculating Capital Gains Tax

My ex bought property A in year 2000 jointly with his ex for £25000 and then in 2008 at the time of their divorce, he bought his ex out of the property for £100000. Now we are getting divorced and if he sells the property I want to know that what will be the bought price when calculating the CGT. This is not his main home it’s a buy to let property. He has got 1 more property like this.

Hi,
His acquistion cost is 50% of the cost in 2000 and the sum paid to buy out the ex's 50%.  The mortgage has no relevance, when calculating capital gains tax.  How the acquisition is financed does not factor into any capital gains calculations.
Thank you.