Angelina Jolie and Brad Pitt knew they'd be together forever.

The couple - who met on the 2004 set of 'Mr. & Mrs. Smith' - had plans to get married from the start of their relationship, according to the man who designed their engagement ring.

Robert Procop said: "Brad and Angelina are a very romantic couple. They always knew they'd be together forever and get married one day, right from the start."

Robert met Angelina after dressing her for the Oscars years ago and he is currently collaborating with her on a jewellery collection, Style of Jolie, whose proceeds will go to her foundation, Education Partnership for Children of Conflict.

He says her relationship with Brad has matured with time.

He told UsMagazine.com: "The relationship may have been all flying planes and riding motorcycles at the start, but any new relationship is exciting that way.

"Now though, they've settled into this wonderfully strong family unit and it's beautiful how in love they are."

The designer added: "They're both lovely, very talented people that complement each other . . . when you're with them, you can see how strongly in love they are."

Brad turned to Robert for help designing a ring for his bride-to-be. The final result is a piece of jewellery boasting an estimated 16-carat, emerald-cut diamond and worth approximately $500,000.

He teased: "Over the years, I have been entrusted with some wonderful secrets. I'd never share something that should be between two people and that is very romantic and special and something for them."