Somerset have "agreed personal terms" with experienced South Africa seamer Vernon Philander, who is set to join the county on a Kolpak deal in 2020.
The 34-year-old will retire from international cricket at the end of the ongoing Test series against England.
He is currently playing his 61st Test at Centurion and has taken 220 Test wickets for South Africa since his debut in 2011.
Philander's Kolpak deal means he will not be deemed an overseas player.
In a statement, Somerset said although a contract had been agreed with Philander "the official paperwork required to complete the deal is being finalised" with the England and Wales Cricket Board.
He has previously had spells in county cricket with Sussex, Middlesex, Somerset, Kent and Nottinghamshire.
"Vernon is undoubtedly a genuinely world-class performer and we are delighted to have agreed terms with such a talented player," said Somerset director of cricket Andy Hurry.
"When the possibility of signing him presented itself, and considering the challenges that we feel lie ahead of us with regards to achieving our aspirations, we felt that it was too good an opportunity to miss."