Seamless cohabitation

Hi
I was in a short marriage 18 months. Prior to that I was in an on/off relationship with my partner. for 9 years. Before the marriage we were split up completely for 12 months where he rented a flat. I have received a letter from his solicitor that he is claiming that it was not a short marriage and that we cohabited for 9 years up to the marriage, and is therefore claiming for a 10 year marriage.

Can he do this ?

I brought the house fully paid into the marriage and have a child (not his) He contributed nothing toward the mortgage or anything towards the house in any way.

Will be simple enough to refute.

Write back to the solicitor pointing out that he was living at xxxx address on xxxx dates.

At the end of the day his solicitor only has the information the client has given them.