Healius Ltd (ASX: HLS) shares are ending the week deep in the red.

In morning trade, the ASX 200 stock is down 30% to a 52-week low of $1.07.

As a comparison, the benchmark ASX 200 index is up 0.15% at the time of writing.

Why is this ASX 200 stock crashing 30%?

The good news for shareholders is that today's massive decline in the Healius share price is not because of a bad update nor a broker downgrade.

In fact, today's big decline could arguably be good news for them.

That's because the decline has been driven by the healthcare company's shares going ex-dividend this morning for a very special dividend.

When a share goes ex-dividend, it means that the rights to an upcoming dividend payment are now settled. As a result, anyone buying this ASX 200 stock today will not be entitled to receive the Healius dividend when it is paid to shareholders. Instead, it will stay with the seller of the shares even though they no longer own them.

In light of this, a share price will usually drop to reflect this. After all, you don't want to pay for something that you won't receive.

The Healius dividend

Earlier this week, Healius announced plans to pay a special dividend following the completion of the sale of Lumus Imaging to funds managed by Affinity Equity Partners.

The ASX 200 stock received cash proceeds of $822 million, which represented an $965 million enterprise value when adjusted for the repayment of equipment leases and closing adjustments.

Net proceeds are expected to be in excess of $800 million after all transaction fees, separation costs and other fees.

Unfortunately, not all of these funds will be returned to shareholders, but a good portion will be.

The ASX 200 stock is returning $300 million to shareholders through a fully franked special dividend of 41.3 cents per share. Those franking credits equate to 17.7 cents per share or approximately $128 million.

Based on where the Healius share price finished yesterday's session, this equates to a stunning 26.8% fully franked dividend yield.

To put that into context, a $5,000 investment in its shares yesterday would generate approximately $1,340 in dividends.

When is pay day?

The ASX 200 stock's eligible shareholders won't have to wait long for pay day.

The healthcare company is planning to pay this monster dividend to shareholders in two weeks on 23 May.