Merge columns based on condition in Rstudio

I want to merge two columns, lat.x and lat.y, so I get a new column, lat.

Data:

lat.x    lat.y    lat
  1        1       1
  2        2       2
 NA        3       3
  4        NA      4
  5        6       5

I've tried:

df2$Lat <- ifelse(df$Lat.x == "NA", df$Lat.y, df$Lat.x)