Return the last day of a given month

[IronCladRooster]

Hello all,

I'm sure there is a nice easy solution to this problem, but for whatever reason I've got a Monday brain and can't come up with a proper solution!

So I have a table with three columns. The first is the year of the item and the second is the given month. I need to fill in the third column with the date of mm/<last day of given month>/yy

I can't figure out a way to have Excel return the last day of the given month in a formula.

See attached for a quick demo of what I'm looking at.

Thank you very much in advance for your help!