Justin Timberlake: 'Working With Madonna is my Biggest Achievement'

Justin Timberlake says working with Madonna was everything he hoped it would be.

The SexyBack singer -- who collaborated with the Material Girl hitmaker on her smash hit single 4 Minutes -- counts recording a song with Madonna as one of his biggest achievements.

He says, "Working with her was definitely a dream of mine.

"And when it came to actually doing it...It was everything you'd think it would be!

"It was great and it was bad and it was cool and it was tedious sometimes and it was fun and we went down into the valleys together and we came out on top of mountains."

Justin -- who is currently dating actress Jessica Biel -- also revealed that he and Madonna became closer after working together.

He added to Britain's Hello magazine, "We had a really good time. And I'm now very happy to be able to call her a friend.

"[Madonna] is a really, really special person."