Paying capital gains on 2nd property with relationship break

[XMES RUS]

As the title asks, partner has moved out some months back but has own flat. If they sell the flat do they still pay capital gains on the sale ? Would we need to get a legal separation to get round this ? Or is it what it is and have to pay.
Views welcome

Btw there is no transfer of asset. It's always been owned by wife and not me.

Edited by XMES RUS on Wednesday 21st September 18:29