Title: 천일의 약속 / Cheonileui Yaksook
Also known as: Forget Me Not
Director: Jung Eul Young
Screenwriter: Kim Soo Hyun
Genre: Romance, melodrama
Episodes: 20
Broadcast network: SBS
Broadcast period: 2011-Oct-17 to 2011-Dec-20
Air time: Monday & Tuesday Night 21:55
Language: Korean
Country: South Korea
Subtitles: English (credit to DramaFever)
Main Cast:
Kim Rae Won as Park Ji Hyung
Soo Ae as Lee Seo Yeon
Lee Sang Woo as Jang Jae Min
Jung Yoo Mi as Noh Hyang Ki

Synopsis:
"A Thousand Days' Promise" tells the story of a woman losing her memory and a man who loves her unconditionally.
Lee Seo-Yeon (Soo-Ae) and Park Ji-Hyung (Kim Rae-Won) have known each other since they were teenagers. Lee Seo-Yeon lost her father when she was only 5-years-old and her mom left her when she was 6. Seo-Yeon was left behind with her younger brother Moon-Gwon. Her aunt took them in and raised in her home.
Seo-Yeon first met Ji-Hyung through Ji-Hyung's long time friend Jae-Min (Lee Sang-Woo), who is Seo Yeon's cousin. During this time Seo-Yeon and Ji-Hyung were just acquaintances.
Now as adults, Ji-Hyung is 32-years-old and his fiancee is Hyang-Ki (Jung Yoo-Mi). Their marriage is arranged by their parents. Seo-Yeon has moved out of her aunt's home and lives with her young brother Moon-Gwon. One year ago, Ji-Hyung and Seo-Yeon's relationship developed, even though Seo-Yeon knew Ji-Hyung was engaged. They promised to see each other until Ji-Hyung married. One year later, Ji-Hyung and Hyang-Ki's wedding date is set. Ji-Hyung and Se-Yeon say their goodbyes to each other...