Are Dianna Agron and Alex Pettyfer Engaged?

Their reps are mum, but a source tells PEOPLE the I Am Number Four costars plan to tie the knot

Source: http://feeds.people.com/~r/people/headlines/~3/uUdaLtTlNjw/0,,20463521,00.html

Kristanna Loken Kristen Bell Kristin Cavallari