Kristen Bell has said that ''vulnerability'' is a key factor in keeping her relationship with Dax Shepard ''healthy''.

The 37-year-old actress has been married to the fellow Hollywood star - with whom she has two daughters Lincoln, four, and Delta, three - since 2013, and on Wednesday (14.02.18) she shared her top tips for keeping romance alive with her followers on Instagram.

Kristen posted a photo of a hand-written note on the site on Valentine's Day, which detailed the six key points which help her keep things running smoothly with her 43-year-old spouse.

The note read: ''Vulnerability always begets connection and intimacy. Stay vulnerable with each other.

''In 10 years, when the dopamine has waned, remember: life is a crazy ride. It's a privilege to go through it with a partner.

''Take necessary separateness. It will make your marriage better.

''Loving someone despite their faults, failings, or character defects, is the most powerful loving thing you can do.

''Rejoice in what makes the other person happy, and allow them their individual interests.

''Know that everyone is doing the best they can with that they've got. So get a bigger emotional tool box to fix your problems.''

The 'Frozen' actress captioned the sweet note with a message explaining she was sharing her ''wisdom'' after attempting to write a congratulatory note to a newly married couple.

She wrote: ''I received a letter from a nice man who asked if I could write a note to his friends who are getting married. I wrote something congratulatory but then thought ''Kristen! Wait! You are an old married woman, shouldn't you have some wisdom to share?!'' After I was finished I realized what I wrote is pretty much the A-Z of how @daxshepard and I keep our relationship healthy. Its worked for us so far, So here ya go. #happyvalentinesday (sic)''