He will remain as an MP in London.
DUP Leader Jeffrey Donaldson's resigned from the Stormont Assembly, but will stay on as an MP in London.
Emma Little Pengelly has been co-opted to fill the vacant seat in Lagan Valley.
The DUP says it won't form a joint government with Sinn Fein until its concerns over the Northern Ireland Brexit protocol are addressed.
Meanwhile, the British Foreign Secretary earlier said there would be "no choice but to act" if no agreement can be reached to change the post-Brexit trade deal.
EU Commission Vice President Maros Sefcovic insists there will be no re-negotiation:

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