what were you doing for 20 years ? if he has remained in possession for 20 years with your knowledge he will raise issue of adverse possession in his defence .

anyhow no harm in trying to regain possession . you must be having original documents in your possession showing area of your land and the boundaries . better contact a local lawyer and file suit against him to direct him to demlish encroachments made in your land . also file criminal complaint against him .