Former deputy Democrat Party leader Trairong Suwannakhiri has resigned from the party, saying he wants to support a new political outfit that shares similar ideologies.
Mr Trairong posted on Facebook that he had assigned his personal secretary to tender his resignation at the party's headquarters on Thursday.
Mr Trairong was elected as a Democrat MP for Songkhla several times and served as a former deputy prime minister during the Abhisit Vejjajiva administration.
He was a member of the party's advisory panel, the last post he held before his resignation after 38 years with the party.
Sources said that following his resignation, Mr Trairong is tipped to join the Ruam Thai Sang Chart Party led by Pirapan Salirathavibhaga, who is also a former Democrat MP.
Mr Pirapan also serves as an adviser to Prime Minister Prayut Chan-o-cha.
Ruam Thai Sang Chart is widely seen as a backup party for Gen Prayut even though he denies any political association with it.
Mr Trairong wrote on Facebook that there are other parties whose ideologies also appeal to him and he wants to be able to support them.
Some parties were set up by former Democrats who quit the coalition party for various reasons. "When they founded new parties and declared party manifestos and policies, they appealed to me, and I wanted to support them," Mr Trairong wrote.
"I want to be myself towards the end of my political career so I can support new parties and express myself freely and openly without having to act secretly as a rebel against the Democrat Party.
"I still support the Democrat Party's ideologies, but I also want to back other parties which share my ideologies," Mr Trairong wrote.
"There are at least five new parties seeking my advice," he added.
Deputy Democrat leader Niphon Bunyamanee on Friday confirmed Mr Trairong's resignation, saying the party has to respect his decision. Mr Niphon insisted that there was no conflict between the party and Mr Trairong.
"We regret it whenever key party members quit. But we have to respect their decisions," Mr Niphon said.
Asked if Mr Trairong's resignation will have an impact on the party given the upcoming election, Mr Niphon said that the party has to carry on and give new-generation politicians a chance to steer it forward.