J.K. Rowling has urged actor Matthew Lewis to ''put some clothes on''.

The 'Harry Potter' author was left shocked after she spotted the 25-year-old star - who played Neville Longbottom in the popular series of films - wearing minimal clothes in the latest issue of Attitude magazine, insisting he covers up in future.

Taking to Twitter, she wrote: ''I will always support you whatever you want to do, Matthew. Now go put some clothes on.''

The 49-year-old writer - who is currently working on the script for 'Harry Potter' spin-off film 'Fantastic Beasts and Where to Find Them' - admitted the risqué shoot wasn't as bad as when the franchise's lead actor Daniel Radcliffe bared his genitals in an on-stage version of the play 'Equus' on London's West End.

She added: ''Not as bad as watching Dan in Equus, but close. Warn me next time, for God's sake.''

And although the author - who has children Jessica, 21, David, 12, and Mackenzie, 10 - caught a glimpse of the provocative photos, she insisted she ''wouldn't know'' if he looked good in the snaps as she quickly turned away.

Replying to another Twitter user who referred to Matthew as ''Neville Pertbottom,'' she joked: ''I wouldn't know. I hastily averted my eyes and read an article on Political Correctness to get over the shock.''