IU & Byun Woo Seok: K-Drama Couple's Happy Ending

In the final episode of MBC's Friday-Saturday drama 'The Grand Prince of the 21st Century,' Grand Prince Ian (Byun Woo-seok) abolished the monarchy and had a happy ending with Sung Hee-joo (IU). Having ascended the throne, Grand Prince Ian declared the abolition of the monarchy, stating, "I will abolish the royal family. Nobility, being born into a certain status, that's where privilege and restrictions begin, and it starts with the royal family." Sung Hee-joo supported this, saying, "I thought it was treason, but it was a revolution." Grand Prince Ian asked, "Are you ready to let go of something you barely possess?" and Sung Hee-joo replied, "When did I ever say I wanted status? It was the missed opportunities because of it that were so frustrating."

Grand Prince Ian's declaration to abolish the monarchy was met with strong opposition from royal relatives. Prime Minister Min Jung-woo (Noh Sang-hyun) also opposed the abolition of the monarchy during a meeting with the relatives, exerting pressure. At this point, Sung Hee-joo appeared and revealed, "Is that why you tried to kill him? You tried to assassinate the king simply because he intended to abolish the royal family, which exerts influence in economy, diplomacy, and culture?" When Grand Prince Ian asked Min Jung-woo if he had tried to kill him, Min Jung-woo admitted it and said, "I begged you. I told you several times to just push Hee-joo far away, and then I would protect you. It's your fault. It's your fault I ended up like this." Grand Prince Ian retorted, "It's your fault for thinking you lost something you never had."

Afterward, the abolition of the monarchy was carried out through a public vote. Three years later, Sung Hee-joo returned to Castle Beauty and took over Castle Card in place of her brother. Grand Prince Ian returned to his original name, Lee Wan, and after settling the royal assets, established a foundation. Sung Hee-joo and Lee Wan returned to being an ordinary couple. When Lee Wan's proposal plan was discovered, he asked, "Don't you want to wear a wedding dress?" Sung Hee-joo replied, "I already did once. I was sincere then, but it seems you weren't?" Lee Wan confessed that he had liked her since the first time he told her his name and kissed her. Afterward, the two shared a kiss at a baseball stadium, marking a happy ending.

Meanwhile, Prime Minister Min Jung-woo applied pressure by withholding royal budget payments, but Sung Hee-joo countered by donating an amount exceeding one year's budget in the name of her family's Castle Group. Min Jung-woo made a strong move by investigating Castle Group's slush funds, but it failed due to the defense of Sung Hee-joo's father, Sung Hyun-gook, and her brother, Sung Tae-joo.

Furthermore, Choi Hyun (Yoo Soo-bin) and Do Hye-jung (Lee Yeon), who stayed by Sung Hee-joo and Grand Prince Ian's side, opened up to each other, hinting at the formation of a new love line. Sung Hee-joo's relationship with her family also changed, with her father Sung Hyun-gook, brother Sung Tae-joo, and sister-in-law Han Da-young all genuinely showing concern for her and expressing family affection.