|Carey Mulligan and Marcus Mumford|
A source told RadarOnline.com: "Carey and Marcus are counting down the days till they tie the knot! She is absolutely walking on air and can hardly contain her excitement.
"It's going to be an amazing weekend as they will be surrounded by their closest family and friends. It's a dream come true for Carey."
The pair first hooked up when Marcus performed in Nashville, Tennessee, just a few months after Carey split from ex-boyfriend Shia LaBeouf.
An insider said: "Marcus invited Carey to watch him play a secret show in the basement of his friend Mike Harris's home in Nashville.
"She sat in the front row and while he was singing Marcus looked down at Carey and she blushed. It was clear they had chemistry.
"Afterwards they went to the City House restaurant and dined with friends but they sat together and acted like a couple."
But despite their whirlwind romance, the future Mr. and Mrs. Mumford are certain they want to spend the rest of their life together.
The source added: "They don't care that some of their friends think they are rushing things. They are madly in love and know they are perfect for each other."