Stamp duty on separation

[Longchip]

I’m buying my ex (unmarried) out of our jointly owned house. I’m paying 80k for their share. The outstanding joint mortgage is 350k but I will pay off around 200k of this before putting it in my own name. The house is valued at 800k.
How much stamp duty will I have to pay on my partner’s share being transferred to me?

I didn’t pay any stamp duty to buy my ex out.

www.gov.uk/guidance/sdlt-transferring-ownership-of-land-or-property#if-you-transfer-or-divide-up-jointly-owned-property-or-land-unmarried-couples-and-other-joint-owners

No stamp duty in that instance,