Nominating Main Residence Upon Change in Ownership

My husband and I have lived in our jointly-owned house since 2000. About 15 years ago, he purchased a nearby flat as a retirement project, which we currently use daily as extra living space. For some unknown reasons, he has ended up as its sole owner. He now agrees to change its ownership to "joint tenants," to include me. Once this has been finalised, can we nominate the flat as our main residence? Thank you.

Hi,
Please refer to the following link:
CG64470 - Private residence relief: only or main residence: an interest in a dwelling-house is a requirement
to see if you meet the qualifying conditions.
Thankyou.