MIL who finds out baby's gender behind parents back may well be the worst MIL in history.

We’ve all heard tales of meddling mothers-in-law.

The one who knows where the spare key is and lets herself in to her son and daughter-in-laws’ home all the time.

The one who expects every Christmas to be spent with her, every Mother’s Day to be about her.

The one who demanded the rights to the first-born’s middle name.

You think your mother-in-law is bad? Well, I’m not sure you can top this.

Deep in the depths of the internet is one of the worst cases of meddling mothers-in-law we've ever seen.

A woman who calls herself “Sad Mommy” has turned to Slate’s Agony Aunt Dear Prudence asking for advice after her mother-in-law found out the sex of her unborn grandchild and told all of the woman’s family and friends, against her wishes.

“Sad Mommy” writes that she has had six years of marriage to an “amazing man” and had a “cordial relationship” with his mother.

“I am now pregnant with his family’s first grandchild,” she explains

“ My husband and I mutually decided that we didn’t want to know the sex before the birth.”

But “Sad Mommy” explains her mother-in-law wasn’t happy.

“My mother-in-law was livid with our decision, even though I tried to placate her by using the obstetrician she suggested and allowing her to attend some of my prenatal appointments. She continued to bring up gender at every opportunity.”

She says that the medical staff at the practice were aware they didn’t want to know, “but after one sonogram I was surprised to see my mother-in-law at the office smiling ear to ear.

“A few days later I had messages from family members congratulating me on the baby girl I was having! My mother-in-law wheedled the information out of the ultrasound technician, who is a friend of hers, then announced it.

“I threatened the clinic with legal action and found a new doctor mid-pregnancy. My mother-in-law is smug about her tactics and told me nastily that if I “still had a mother,” I wouldn't be so selfish. (I was orphaned at age 14.)"

“Sad Mommy” says she feels betrayed and hurt.

“My husband sides with me and we’ve made a birthing plan that includes her not being permitted in the facility until we’ve been released. We will not inform anyone of the birth until after we're home, and for the time being, she won't be welcome to visit.”

But she wonders if her actions go too far.

“Am I being too vengeful here? How do I overcome this feeling of betrayal?” she asks.

It’s not the first time we’ve heard stories of mothers-in-law overstepping the boundary.

We’ve heard before of one mother-in-law who called her new daughter-in-law by her sons' former wife's name for three years. Until she divorced.

We’ve heard of the mother-in-law who booked, paid for and then went along to her son and daughter-in-law’s honeymoon.

And now this mother-in-law.

So what’s the answer? Should ‘Sad Mommy’ just cut her mother-in-law and future grandmother out of their lives?

Agony Aunt Dear Prudence, whose column is syndicated to over 200 newspapers across the US, told her that her privacy had been violated and she has every right to be angry,

“I guess you could consider yourself lucky your mother-in-law didn’t pop out of the closet while you and your husband were trying to conceive, like one of those terrifying mothers in the Old Spice commercials,” Dear Prudence writes.

“But how utterly unnerving to have found her lurking at your doctor appointment. After the technician violated your privacy, you were right to have found another practitioner.”

She tells ‘Sad Mommy’ how lucky she is that her husband is supporting her.

“Too often, I hear about sons of such mothers who have been trained since childhood to give in to these termagants, and who find it easier even in adulthood to avoid the drama and accede to their demands.”

More confessions, the worst thing ever said to a mother-in-law. Post continues after video..

“Your mother-in-law,” she writes, “has proven herself unable to distinguish between her desires and someone else’s. Given her remark to you about your deceased mother, she is also cruel and insensitive. Your husband should explain to his mother that because of her behaviour during your pregnancy you two are on hiatus from her. Say that it would be sad not to have her in your child’s life, but if she wants to enjoy being a grandmother, a basic requirement is that she treat her daughter-in-law with respect.”

“An apology from her and a recognition she needs to do better would be a start. But in the absence of that, after the baby is born and you feel ready, allow her some short visits to see if she seems capable of reform. You’re not being vengeful; she’s the one who has to regain your trust. And don’t let her terrible behaviour make you engage in a stealth birth. You and your husband shouldn’t feel that becoming parents is something to keep clandestine.”

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