Is it hard to learn how to play the mandolin?

I decided I want to learn how to play the mandolin after seeing my
friend play his. I really liked the sound of it and he told me that he
taught himself how to play, but he also plays the guitar and the
violin.

I have no experience with any string instruments. The only instrument
I play is the flute, which probably won't help me at all.

So how hard do you think it will be for me to learn how to play the
mandolin?