All 40 year old's will be let in to Dublin Zoo for free on Saturday week to coincide with an orangutan's birthday.
Sibu - a Bornean orangutan - is also turning the big 4-0.
Now for 39 or 41 year old's who feel they might look 40 - Valid photo ID must be presented at the gate.
The good news doesn't stop there, kids will also be allowed into the zoo for half-price on November 24th to celebrate Sibu's big day.
They'll be able to take part in an afternoon of arts and crafts, and play some orangutan games.
Money will also be collected on the day for the Orangutan Foundation which works to protect their tropical forest habitat.