Although his last album has underperformed, he has continued his popularity by becoming a mainstay on KBS's Heroine 6, becoming part of the "Gag Team 3" with Shin Jung Hwan from Country Kko Kko and Kim Jong Min from Koyote.

[3][4][5] Lee released his 10th anniversary album 'Synergy' in November 2013, including title track "We Loved Together", which is composed and written by 5 o'clock and features Ha Dong Kyun.

The album also includes "Doesn't Make Sense" which was written by Lee Jand composed by both Lee and Jo Jung-chi as well as his previous digital single, "I Am Sorry" which received attention for being the work of Brave Brothers, "Did You Ever Love" and "Let's Stay Together".

[6] In July 2015, Lee made an appearance under the pseudonym of 'Tungki' on MBC's King of Mask Singer.

Tungki came out guns blazing, eliciting a standing ovation from the judges and cheers all around, with a powerful performance of Kim Kyung Ho's “People Who Make Me Sad.” With that performance he successfully toppled 'Cleopatra' AKA Kim Yeon Woo who until then had enjoyed a record 10-week long rein as the King of Mask and solidified his reputation as one of Korea's most skilled vocalists.