Former Democratic Party(DP) leader Lee Nak-yon officially announced on Thursday his departure from the party to form a new one.

The announcement was made at the National Assembly Communication Hall, where Lee said he decided to leave the party he was a part of for 24 years and embark on a new path to serve the country.

The ex-DP chief said South Korea must change its political structure as he believes that the country cannot prosper without breaking the current two-party duopoly.

Lee said he will first work closely with a trio of non-mainstream lawmakers called "Principles and Common Sense" who recently left the DP.

Reps. Cho Eung-cheon, Kim Jong-min and Lee Won-wook all left the main opposition party this week, while the fourth member, Yoon Young-chan, opted to stay with the party.