Who is making an appearance?

Sylvester McCoy, the seventh Doctor, at a convention in New Zealand, stated that Peter Davison was going to appear in a multi Doctor episode in season four.

Seventh Doctor Actor Sylvester McCoy released a possible spoiler at the Day With A Doctor event in Auckland, New Zealand. McCoy sited the source of the information as Peter Jackson. There has been no Official Announcement of this from the BBC.

McCoy claimed that Fifth Doctor Peter Davison is due to return for Series 4 in a Multi-Doctor episode.

That would be awesome. Peter Davison was always my favorite Doctor.