CGT Query - Second home bought 'first'

Me and my partner purchased my parents home (house 1) some years ago (around 2008). At the time, we were renting. In 2020, we bought our current home, which at that point became our main residence (house 2). Both my parents have now passed, and I am trying to understand how CGT will be charged. While House 1 is now my second home, it was my sole property until the purchase of House 2, so is CGT still calculated from the time of purchase, even though it hasn't been a second home for the entire period? Any clarification would be appreciated.

Hi,
It is based on the difference in value at time of purchase to date sold. You can then claim private resident relief for the period you lived in it to reduce the tax due - Private Residence Relief (Self Assessment helpsheet HS283)/HS283 Private Residence Relief (2024).
Thank you.