千古遗恨

to have eternal regrets (idiom)

thousand

see 鞦韆|秋千[qiu1 qian1]

for all eternity / throughout all ages / eternity (used in an elegiac couplet, wreath etc dedicated to the dead)

surname Gu

ancient / old / paleo-

to lose / to leave behind / to omit / to bequeath / sth lost / involuntary discharge (of urine etc)

(bound form) to leave behind

eternal regret

to hate / to regret