Reese Witherspoon feared she would wet herself on set while working with Vince Vaughn.

Dismissing rumours there was friction between her and her comic co-star on new movie ?Four Christmases?, the actress claims it was the most fun she?s ever had making a movie.

She said: ?Vince is the funniest person I've ever worked with in my entire life.

?There were days when we were shooting things, I would laugh so hard it would ruin the take, and I was afraid I was going to pee myself, it was so funny.?

Witherspoon ? who has two children, nine-year-old Ava and four-year-old Deacon, with ex-husband Ryan Phillippe ? also revealed she is ?very happy? with boyfriend Jake Gyllenhaal.

The Oscar-winning actress admits it is a great comfort to be in a relationship with such a loyal partner.

Witherspoon (32), added to America?s Vogue magazine: ?Jake is very supportive.

?Suffice to say, I'm very happy in life and I'm very lucky to have a lot of really supportive people around me who care very much for me. You know, that's all you can hope for in life. I am very blessed in that way.?