The pair are England teammates - and rivals.
"As a person, he's fantastic. If ever you wanted to be happy for someone coming down from north of the border to take his chance in the Premier League and be a success, it would be him," said Foster.
"He is one of the nicest guys you will ever meet in football - an absolute star. He's certainly shown what he can do and I'm delighted for him.
"We're very good friends and if he was local to me, we'd be even bigger mates. We always talk on the phone and text each other. We get on really well with England and Joe Hart is a big part of that as well, to be fair.
"Southampton have shocked everybody. I think everyone had them down as favourites to get relegated with selling so many top players."