Sources: Telegraph Nepal and Nepal public holidays (qppstudio.net). It is reported that the government of Nepal is planning to declare a 3-day public holiday on the occasion of the upcoming Constituent Assembly Convention, the first ever, on May 28, 2008, at which convention it is expected that the CA will formally declare Nepal a federal democratic republic, thus ending 240 years of monarchy.
Update, May 27: This has now been confirmed.