The Undertaker will be appearing at the SmackDown taping on April 23rd from the O2 Arena in London, England. Here is the statement from the official website of the arena:
The Undertaker returns to London!
This is a London exclusive NOT to be missed!
It is not known whether The Undertaker will be appearing on television, or just for the local audience. As of this writing, he is not scheduled for RAW the night before at the same arena.