Philippine Republic Day, why?

There was a column in The Dallas Morning News concerning Philippine Republic Day which is on June 12th. The column stated the Philippines received their independence from the United States on July 4th, 1946, and celebrate independence on June 12.

Good journalist use to be trained to answer the following in all news articles:
who,
what,
when,
where,
why, and
how.

This article did not answer "why." As to why do they celebrate their independence on June 12, when July 4th was their day of independence form the USA?

Checking the Internet: It was on June 12th, 1898 when the Philippines wrote their Declaration of Independence from Spain, as the Philippines was a colony of Spain. That is why the Philippines celebrate their independence on June 12th, and not July 4th.