A copy of a photo of Sun Yat-sen and Soong Ching Ling taken in Kobe in 1924 is one of the rare exhibits on display at the National Museum of China. [Photo provided to China Daily]

The day after they registered their marriage in Tokyo on Oct 25, 1915, the great revolutionary Sun Yat-sen who died in 1925, and the late Soong Ching-ling signed a pledge.

In the document written in Japanese at a lawyer friend's house, they promised to complete the Chinese legal procedure for marriage as soon as possible, try to keep each other happy and raise no objection to legal or social punishment for violating the pledge.

Despite a 27-year gap in age between them and strong opposition from Soong's family and Sun's fellow revolutionaries, the wedding took place.

Sun, who had a divorce before he married Soong, said that he wouldn't regret it even if he died the day after he married her. And, she in turn said nothing would bring her greater happiness than accepting his proposal. She believed it was also a way to dedicate herself to the Chinese revolutionary cause.