Friend in different realm

They can not do it from this post.
Follow the instructions here Realm Transfer Process
You need to meet the might requirements for the realm you intend to join. If you don't, your friend will need to join yours...and don't forget to tell ATA the exact username of the person whose realm you want to join (assuming you meet the maximum might requirements to join their realm and haven't exceeded the transfer limits.)

Make sure to ask in game via the help feature.

 

You are going to have to follow this link. Realm Transfer Process
They update it constantly, so if I post what it says today, it may change tomorrow.