Mark, who had been at the Upper Chamber since 1999, was sacked late last year when the Court of Appeal ordered a rerun poll for his Senatorial District .
However at the rerun poll, he defeated Daniel Onjeh of the All Progressives Congress(APC) to clinch the seat of the Benue South Senatorial District penultimate Saturday.
The arrival of Mark to the floor around 11.am was heralded by standing ovation by all Senators present excluding Senator Shehu Sani (APC, Kaduna central) and Senator Isiaka Adeleke (APC, Osun West) that remained seated.
It was the PDP Senators that first stood up to welcome Mark, before their APC colleagues and Saraki joined. But Sani and Adeleke remained on their seats.
Soon, the chatting of the "the youngest and most ranking Senator" dominated the floor. Mark is the longest serving Senator, he has been at the Red Chamber since 1999.
It was observed that immediately after he was sworn in, Mark went round to shake his colleagues. He hugged Senator Barnabas Gemade (APC, Benue North-east).
Afterwards, Mark went straight to his former seat. Before his election was nullified, Mark's seat was situated at the last row of the section of the PDP.
Our correspondent reports that the sitting arrangement of the Senators is based on ranking/ seniority with most senior or ranking Senators sitting on first row or next to principal officers.
Also sworn in was Ahmed Salawu for the Kogi Central. Salawu is a PDP candidate like Senator Mark. He replaced Abdulsalami Ohiare of the APC.
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