Deleting duplicated rows based on condition (position)

I have a dataset that looks something like this

df <- data.frame("id" = c("Alpha", "Alpha", "Alpha","Alpha","Beta","Beta","Beta","Beta"), 
                 "Year" = c(1970,1970,1970,1971,1980,1980,1981,1982), 
                 "Val" = c(2,3,-2,5,2,5,3,5))

I have mulple observations for each id and time identifier - e.g. I have 3 different alpha 1970 values. I would like to retain only one observation per id/year most notably the last one that appears in for each id/year. the final dataset should look something like this:

final <- data.frame("id" = c("Alpha","Alpha","Beta","Beta","Beta"), 
                    "Year" = c(1970,1971,1980,1981,1982), 
                    "Val" = c(-2,5,5,3,5))

Does anyone know how I can approach the problem?

Thanks a lot in advance for your help