South Africa batsman Alviro Petersen has signed a short-term deal with Essex for the beginning of the 2012 season.
The former Glamorgan captain had hoped to re-sign with the Welsh county after his successful 2011 campaign but the two parties could not agree terms.
And Petersen, who has cemented his place in the South Africa Test team with some fine performances against Sri Lanka, has agreed to join Essex instead.
Glamorgan are trying to find a replacement and are being linked with Australia all-rounder Moises Henriques.
Petersen wrote on Twitter: "Delighted to have signed a short term contract with Essex CCC from the start of the season until mid-June 2012.
"My agent gave Glamorgan a proposal which they didn't accept. Would have loved to join Glam!
"Glammy can only sign one overseas. We proposed something but Glammy rejected such.
"Just to put the record straight, I enjoyed my time with Glamorgan, and yes, would have wanted it to continue.
"They played a massive part in my success at international level. Great fans, good people! I thank all involved."