David Schwimmer and Jennifer Aniston. (WENN.COM)

'Friends' star David Schwimmer is reportedly fuming with his former co-star Jennifer Aniston after she insisted on U.S. TV that she doesn't know who his fiancee is.

Schwimmer announced he is set to wed his girlfriend of two years Zoe Buckman earlier this month.

But the actor was allegedly left humiliated when Aniston appeared on David Letterman's show and told him she had "no idea" who her longtime pal was marrying.

Now Schwimmer is reportedly refusing to speak to Aniston over the comment, according to Britain's Mail on Sunday.

A source tells the publication, "David was not impressed that one of his supposed friends didn't know who he was marrying. He has been with Zoe for a couple of years and was offended Jen couldn't remember her. He hasn't been taking her calls."