Buying a 50% share of husband to be's house, implications for stamp duty on a second home

Shookup

Would I have to pay stamp duty if I purchased a 50% share of my soon to be spouse's property as a second home?  We are marrying in July.  We intend to keep both our properties whilst we are married but I am interested in buying a 50% share of my fiance's house (without selling my own house). 

The reasoning behind this is to be able to release some equity from the property for his grown up son who is looking to buy and would prefer to receive his inherited share of the house now, rather than wait. My fiance's other grown up son still lives in the house and is not in a financial position to leave home.   My children are younger than my partner's and so do not need help yet.  

SDLT_Geek

If you buy the share once married, then a special rule would mean that the 3% SDLT surcharge would not apply to your acquisition, even though you have another property.

Shookup

Thanks.  I was looking it up and I couldn’t work out if it being a second home meant the stamp duty would apply