R: Legend not showing in ggplotly map

I have made a map with ggplot which shows points on the map with different sizes based on the Freq value in my dataframe:

Longitude   Latitude    Result  Freq
4.690000    51.97400    Neg    1
6.040604    51.66494    Neg    23
6.87448     52.31593    Neg     4

My ggplot code:

TestObject = ggplot() + 
            aes(long,lat, group=group), 
            color="black", size=0.3) +
  theme_opts + 
             aes(x=Longitude, y=Latitude, size=Freq),
             colour="red", fill = "violetred2", pch=21, alpha=I(0.65)) + 
  scale_size(range = c(3,10)) 

“Neth” is my downloaded GADM map. This is how my ggplot looks with my actual data:

When I use ggplotly on this ggplot then my legend which indicates point size goes away:

ggplotly(TestObject, width=700, height=700)

This is how my ggplotly ends up looking:

Any way to add a legend to this ggplotly or a way to maintain my ggplot legend?