SDLP leader Colum Eastwood has tweeted that a Lisburn and Castlereagh City councillor has transferred from the Greens to his party.
Simon Lee, who represents Castlereagh South, has changed his twitter bio to reflect the move.
He was first elected to the council as a Green Party member during the 2019 local council elections.
During May's Northern Ireland Assembly election the Green Party lost both of its seats which had been held by Claire Bailey (South Belfast) and Rachel Woods (North Down).
Colum Eastwood posted on Twitter that he was "delighted" that Mr Lee had joined the SDLP.
In a statement issued by the SDLP, Simon Lee said the move had been a "big decision" but that it "feels like the perfect fit".
“Over the last number of years I’ve also been more attracted to the party’s work on building a new Ireland," the statement added.
The Castlereagh South representative was also welcomed by SDLP MP Claire Hanna, who tweeted that Mr Lee's "politics are a sound fit" with the party.
"We’ve worked together on issues relating to the environment, public services and more over recent years," she added.
"Simon is a real champion for Carryduff and a great addition to our team."
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