Principle residence exemption

I’ve just sold a flat. We (ex boyfriend and I) had owned it for 16.5 years. We lived in it together for about 4 years and then he lived in it for about 4 years with a lodger, when it was also my uk residence but I was also working abroad. It was rented out for the last 8 years. I was looking and we don't have any evidence anymore from beyond the last 8 years when it was rented out. How do we prove this and also how do I work out if we are eligible for any principle residence exemption? Is he eligible for more PRE than I am? Or can we claim PRE of 50% because it was only rented out for approximately 50% of the time we owned it. We have no other properties. Thanks very much.

Customer name andt & email removed admin .

Hi hannahroberts,
Please refer to guidance here:
Private Residence Relief (Self Assessment helpsheet HS283)
Thank you.