The `Gossip Girl` co-stars called time on their three-year romance last month, a spokesperson for the former couple has confirmed.

Despite their split, the pair have vowed to stay friends.

One source told Us Weekly magazine: "They`re professionals. They`re still good friends and hang out on the set."

News of their separation is said to have shocked their other `Gossip Girl` co-stars as they had kept the news under wraps for so long.

The insider said: "They kept this news to themselves for a while.

"Nobody on set had any idea. They`re really just private."

It has been claimed that Penn, 24, ended the relationship because Blake, 23, was keen to get married and have children and he wasn`t ready.

A source told America`s Star magazine: "Blake comes from a traditional Southern Baptist background, and she`s always had her eye on getting married and having lots of children.

"The pressure on him to settle down at such a young age finally reached the point where he realised he and Blake couldn`t get on the same page, timing-wise, about starting a family."
sections: Celebrities