Am I entitled to a share of my ex-husband’s estate?

An ex-spouse does not by right have an automatic entitlement to make a claim agaisnt the estate.

However, if the ex-spouse can show they were dependent on the deceased - perhaps because they were receiving spousal maintenance - this would evidence dependency and give them a basis to make a claim.

It is important though to check whether the financials were resolved before death. It is not uncommon for a divorce order to contain a bar to an Inheritance Act 1975 claims by former spouses.  

Your husband’s executors, or beneficiaries, could oppose your claim. There might also be competing claims for reasonable financial provision from your husband’s children or step-children, and anyone he was maintaining financially at the time of his death. If he remarried, there may also be a claim from his second spouse.

Don't forget there is a time limit. You need to make sure your claim is made within six months of the date from the grant of probate.