The couple visited jeweler Neil Lane about two weeks ago to pick out an engagement ring – and left the store with two rings, Lane says. "They couldn't decide on one, so they got them both," Lane tells PEOPLE. "Simon told me: 'You know, you only live once.' He did it with a lot of love and sentiment. I've never had that happen to me before. It's so romantic." One was a five-carat platinum ring with a yellow diamond surrounded by white stones, the other was a six-and-a-half-carat platinum ring with a cushion-cut diamond and diamonds embedded into the band. They showed off the both rings – and a wedding band – at the Derby, where they were guests of T-Mobile, along with Jimmy Fallon, Laura Prepon and Regina King. "They were all over each other – very, very affectionate," says a source who saw the couple Saturday morning at a party in Louisville.
Although the only thing that really matters is the ring FYI the fiancee is Simon Monjack, the British writer & director of her latest project.